目錄
Japanese 「どこで」 and 「どこに」 may both look like “where” in Chinese, but they cannot be exchanged freely in a sentence. 「どこで食べますか」 asks where someone will eat, while 「トイレはどこにありますか」 looks for the location of a restroom. Chinese can cover both with one 「在」, but Japanese separates the two situations.
An easier way to remember the distinction is to ask what the place does in the sentence. Eating, shopping, working, and watching a film are events that happen somewhere, so they use 「で」. Asking where a person stays, where an object is placed, or where someone is going often involves 「に」. 「あります」 is slightly more troublesome: a convenience store exists somewhere with 「に」, but a festival or game takes place somewhere with 「で」. The verb alone is not enough; the subject before it must also be considered.
What Are 「どこで」 and 「どこに」? How 「で」 and 「に」 Mark Place
「どこ」 itself only means “where.” The following particle determines the sentence’s direction. 「どこで」 treats a place as the site of an action or event, while 「どこに」 treats it as the location where a person or thing remains or as the final destination of movement.
For example, consider the same place, 「図書館」:
- 図書館で勉強します: study at the library
- 図書館にいます: be at the library
- 図書館に行きます: go to the library
All three sentences contain the same location, but the particles differ. The first asks where 「勉強する」 takes place, the second concerns where a person currently is, and the third treats the library as a destination.
This is the most practical way to distinguish 「どこで」 from 「どこに」. Do not rush to translate the sentence. First check whether the following verb describes an action, existence, or movement.
How to Distinguish the Japanese Place Particles 「で/に」: From Actions to Destinations
Place particles can first be divided into four common relationships. Use 「で」 for the site of an action or event, and mainly use 「に」 for existence, staying, and the endpoint of movement.
| What You Want to Ask | Question Form | Common Verbs/Content | Example |
| Where an action occurs | どこで | 食べる、買う、勉強する、働く、会う | どこで昼ご飯を食べますか。 |
| Where a person or thing is | どこに | ある、いる、住む、泊まる | 駅はどこにありますか。 |
| Where movement is headed | どこに | 行く、来る、帰る、着く | どこに行きますか。 |
| Where an activity or event occurs | どこで | 祭りがある、試合がある、会議がある | どこで試合がありますか。 |
The fact that 「ある」 appears with both 「に」 and 「で」 is the easiest part of this topic to get wrong. 「コンビニがあります」 concerns the location where a convenience store exists, so it uses 「に」. 「コンサートがあります」 concerns where the concert event takes place, so it uses 「で」.
Uses of Japanese 「どこで/どこに」: Actions, Existence, Destinations, and Events
「どこで」|Asking Where Eating, Shopping, Working, and Other Actions Occur
The most basic function of 「どこで」 is to ask where an action is performed. It commonly precedes action verbs such as 「食べる」「買う」「勉強する」「働く」「写真を撮る」.
Answers likewise use 「place+で」. Thus, 「どこで食べますか」 can be answered with 「レストランで食べます」, while 「どこで買いましたか」 can be answered with 「駅の店で買いました」.
- Example: 昼ご飯はどこで食べますか。
Kana: ひるごはんはどこでたべますか。
Translation: Where will you eat lunch?
「食べる」 is a concrete action. The question asks in which place the action of eating lunch will occur, so it uses 「どこで」. - Example: 週末はどこで勉強していますか。
Kana: しゅうまつはどこでべんきょうしていますか。
Translation: Where do you usually study on weekends?
「勉強する」 describes an activity performed in a place. The place is where the action occurs, so 「で」 is used. - Example: このお菓子はどこで買えますか。
Kana: このおかしはどこでかえますか。
Translation: Where can I buy this snack?
Even though the verb is the potential form 「買える」, the sentence still asks where the act of purchasing can be performed, so the particle does not change to 「に」.
「どこに」 Use ①|Asking Where People, Things, and Facilities Exist or Stay
With 「ある」 or 「いる」, 「どこに」 asks where a person or thing is currently located. 「ある」 is used mainly for inanimate objects and facilities, while 「いる」 is used for people and animals.
「住む」 and 「泊まる」 also commonly take 「に」. Although living and staying may look like actions, these verbs emphasize the state of remaining in a place for a period, rather than an ordinary action site marked by 「で」.
- Example: トイレはどこにありますか。
Kana: トイレはどこにありますか。
Translation: Where is the restroom?
The question seeks the location of the restroom facility, not an action taking place inside it, so it uses 「どこに」. - Example: 田中さんは今どこにいますか。
Kana: たなかさんはいまどこにいますか。
Translation: Where is Mr. Tanaka now?
「いる」 marks the location of a person’s existence, so 「どこにいますか」 asks where that person currently is. - Example: 東京のどこに住んでいますか。
Kana: とうきょうのどこにすんでいますか。
Translation: Which part of Tokyo do you live in?
「住む」 focuses on one’s place of residence and therefore uses 「に」. An ordinary question about residence does not use 「どこで住んでいますか」.
「どこに」 Use ②|Asking the Destination of 「行く」「来る」「帰る」 and Other Movement Verbs
With movement verbs, 「に」 marks the final destination. When 「行く」「来る」「帰る」「着く」 appear, 「どこに」 asks for the endpoint rather than a place passed along the way.
This 「に」 does not function exactly like the 「に」 of existence, but both treat the place as a landing point.
- Example: 夏休みはどこに行きますか。
Kana: なつやすみはどこにいきますか。
Translation: Where are you going for summer vacation?
「どこに」 asks for the final destination of 「行く」. - Example: このあと、どこに行けばいいですか。
Kana: このあと、どこにいけばいいですか。
Translation: Where should I go next?
The sentence is not asking for the current location; it confirms the next place to visit. - Example: 空港からどこに向かいますか。
Kana: くうこうからどこにむかいますか。
Translation: Where are you heading after the airport?
「向かう」 means to proceed toward a target, and 「に」 marks the endpoint toward which the movement is directed.
「どこで」 Use ④|Activities, Games, and Events Use 「で」 Even Before 「あります」
Because 「ある」 is often first learned through 「場所に物があります」, learners may automatically select 「に」 whenever they see 「あります」. If the subject is an event such as a game, festival, meeting, class, or earthquake, however, the place is not the static location of an object but the site where the event occurs.
This is why Japanese allows 「公園で夏祭りがあります」「学校で試合があります」「大阪で地震がありました」.
- Example: 夏祭りはどこでありますか。
Kana: なつまつりはどこでありますか。
Translation: Where will the summer festival be held? 「夏祭り」 is an activity, and 「で」 marks where it takes place.
Do not change it to 「どこに」 simply because 「あります」 appears. - Example: 次の試合はどこでありますか。
Kana: つぎのしあいはどこでありますか。
Translation: Where will the next game be held? A game is an event, so the question asks for its venue.
「試合会場はどこにありますか」 instead asks for the location of the venue facility itself. - Example: 昨日、どこで地震がありましたか。
Kana: きのう、どこでじしんがありましたか。
Translation: Where did the earthquake occur yesterday? An earthquake is an event, and 「で」 marks its site.
This is another important example showing that 「あります」 does not always take 「に」.
Japanese 「どこで」 vs 「どこに」: Complete Comparison of Place Particles
Both 「で」 and 「に」 can follow a place, but they view that place differently. 「で」 tends to make the place the area in which something occurs, while 「に」 often treats it as the point where someone or something exists, stays, or ultimately arrives.
| Comparison | 「どこで」 | 「どこに」 |
| Main function | Asks where an action, behavior, or event occurs | Asks where a person or thing exists or stays, or the destination of movement |
| Role of the place | Where something is performed or occurs | Where someone or something is located, remains, or ultimately arrives |
| Common verbs | 食べる、買う、勉強する、働く、会う | ある、いる、住む、泊まる、行く、来る |
| Activity or event | どこで試合がありますか | Normally not used to ask where an event occurs |
| Existence | Normally not used for a simple location of existence | トイレはどこにありますか |
| Destination | Normally does not mark an endpoint | どこに行きますか |
| Basic test | Where does this happen? | Where is the person or thing/where is it going? |
▌「どこで食べますか」 vs 「どこにいますか」: The Same Place Can Take a Different Particle
The place itself does not determine the particle. The following verb changes the relationship between the place and the sentence.
✅ レストランで食べます。
Eat at the restaurant.
✅ レストランにいます。
Be at the restaurant.
The first treats the restaurant as the site of 「食べる」. The second only states that a person is currently at the restaurant.
Places such as restaurants, schools, and companies therefore cannot be classified as always using either 「で」 or 「に」. The same place changes particles with the verb.
▌「どこにありますか」 vs 「どこでありますか」: Existence of an Object vs Occurrence of an Event
「あります」 can indicate both the existence of an object and the occurrence of an activity or event. The type of noun serving as subject directly changes the place particle.
✅ ATMはどこにありますか。
Where is the ATM?
✅ イベントはどこでありますか。
Where is the event being held?
The ATM in the first sentence is a facility, so the question is “Where is it located?” The event in the second is not an object placed somewhere but something that will happen at a location.
Formal event information also often uses the clearer verbs 「行われる」 or 「開催される」.
✅ 花火大会はどこで行われますか。
Where will the fireworks festival be held?
✅ 展示会はどこで開催されますか。
Where will the exhibition be held?
▌「どこで会いますか」 vs 「誰に会いますか」: 「で」 and 「に」 Can Both Appear with 「会う」
「会う」 is useful for understanding why particles cannot be memorized from the verb alone.
✅ どこで田中さんに会いますか。
Where will you meet Mr. Tanaka?
This sentence contains both:
- 「どこで」: where the act of meeting occurs
- 「田中さんに」: whom someone meets
「で」 marks the place and 「に」 marks the other person; the two do not conflict.
- Example: 駅で友達に会いました。Kana: えきでともだちにあいました。
Translation: I met a friend at the station.
「駅で」 is the meeting place, while 「友達に」 is the person met.
When you see 「に」, also check whether it actually marks a place.
▌Why Can’t 「どこに住んでいますか」 Be Decided by “Doing an Action = で”?
「住む」 is certainly a verb, but Japanese does not classify every verb under 「action site+で」.
Verbs of living, remaining, and lodging focus on a person settling in a place and maintaining a state there, so they commonly use 「に」.
✅ 東京に住んでいます。
I live in Tokyo.
✅ 京都のホテルに泊まります。
I will stay at a hotel in Kyoto.
❌ 東京で住んでいます。
Unnatural in an ordinary question or statement about residence.
When describing activities actually performed during the period of residence, 「で」 returns.
✅ 東京で働いています。
I work in Tokyo.
✅ 京都で日本語を勉強しています。
I study Japanese in Kyoto.
▌What Changes When the Same Location Uses 「どこで/どこに」? Action vs Position
The same location can take both 「で」 and 「に」 without contradiction. The difference is whether the question concerns “what happens there” or “whether a person or thing is there.” A restaurant can be the site of eating or simply someone’s current location, so both 「レストランで食べる」 and 「レストランにいる」 are valid.
- Example: 昼ご飯はどこで食べますか。
Kana: ひるごはんはどこでたべますか。
Translation: Where will you eat lunch?
The place is treated as the site of 「食べる」, so 「どこで」 is used. The question seeks an eating location, not the person’s current position. - Example: 今どこにいますか。
Kana: いまどこにいますか。
Translation: Where are you now?
The sentence does not ask what activity is in progress but directly checks the person’s location. 「いる」 describes existence, so it takes 「どこに」. - Example: 駅の近くで友達に会います。
Kana: えきのちかくでともだちにあいます。
Translation: I will meet a friend near the station.
「駅の近くで」 marks where the meeting occurs. Changing it to 「駅の近くにいます」 means “I am near the station,” leaving only location information and no meeting.
Japanese 「どこに」 vs 「どこへ」: Comparing the Destination Particles 「に/へ」
Both 「どこに行きますか」 and 「どこへ行きますか」 mean “Where are you going?” and both sound natural in everyday use.
| Comparison | 「どこに」 | 「どこへ」 |
| Main function | Asks the final destination | Asks the direction or destination of movement |
| View of place | More readily treats it as a definite endpoint | Carries more sense of proceeding in a direction |
| Common verbs | 行く、来る、帰る、着く | 行く、来る、帰る |
| With 「行く」 | どこに行きますか | どこへ行きますか |
| Everyday difference | Small in most basic movement sentences | Interchangeable with 「に」 in most basic movement sentences |
| Existence | Possible, as in 「どこにいますか」 | Cannot mark existence |
| Point of arrival | 「着く」 normally takes 「に」 | 「駅へ着く」 is generally not used |
「に」 more readily treats the destination as a definite endpoint; 「へ」 carries a sense of proceeding in a direction. In basic movement sentences with 「行く、来る、帰る」, however, they are often interchangeable, and the distinction does not need to be exaggerated.
- Example: 明日はどこに行きますか。
Kana: あしたはどこにいきますか。
Translation: Where are you going tomorrow?
「に」 focuses the question on the final destination. - Example: 明日はどこへ行きますか。
Kana: あしたはどこへいきますか。
Translation: Where are you heading tomorrow?
「へ」 carries a sense of movement in a direction, but in ordinary travel conversation the difference from the previous sentence is slight. - Example: 旅行のあと、台湾に帰ります。
Kana: りょこうのあと、たいわんにかえります。
Translation: I will return to Taiwan after the trip.
「台湾へ帰ります」 is also natural. 「に」 and 「へ」 are often interchangeable in basic movement sentences.
▌Using 「どこに/どこへ」 for the Same Destination: Endpoint vs Direction
With 「行く」「来る」「帰る」, 「に」 and 「へ」 can often point to the same destination, and the practical difference in conversation is small. 「に」 more readily draws attention to the final point of arrival, while 「へ」 preserves a slight sense of moving in that direction. This is not a rule of free substitution in every sentence: only 「に」 marks existence, and 「着く」 also normally takes 「に」.
- Example: 明日はどこに行きますか。
Kana: あしたはどこにいきますか。
Translation: Where are you going tomorrow?
「どこに」 focuses on the eventual destination and is natural for schedules and the next stop. - Example: 明日はどこへ行きますか。
Kana: あしたはどこへいきますか。
Translation: Where are you heading tomorrow? It is very close in practical meaning to 「どこに行きますか」; 「へ」 simply adds a slight sense of movement toward a direction.
There is no need to overstate the distinction in ordinary travel conversation. - Example: 旅行のあと、台湾に帰ります。
Kana: りょこうのあと、たいわんにかえります。
Translation: I will return to Taiwan after the trip.
The sentence can also use 「台湾へ帰ります」. With 「に」, Taiwan is directly understood as the destination; 「へ」 leans slightly toward the direction of returning to Taiwan. Both are natural.
Japanese 「どこで/どこに/どこですか」: Three Ways to Ask About a Place
When looking for a restroom, counter, or station, travelers also frequently hear the shorter 「どこですか」.
| Comparison | 「どこで」 | 「どこに」 | 「どこですか」 |
| Main function | Asks where an action or event occurs | Asks an existing location, place of stay, or destination | Directly asks where a person, thing, or place is |
| Needs a following verb? | Yes | Yes | No separate place verb required |
| Common form | どこで食べますか | どこにありますか | トイレはどこですか |
| Asking a facility’s location | Usually no | Yes | Yes |
| Asking an action site | Yes | Usually no | May be shortened this way when context is clear, but contains less information |
| Conversational brevity | Must state the action | Must state existence or movement | Shortest |
| Amount of information | Clearly states where something is done | Clearly states a location of existence or movement | Directly asks only “where?” |
「トイレはどこにありますか」 fully states “Where does the restroom exist?” while 「トイレはどこですか」 directly asks “Where is the restroom?” Both are natural; the latter is shorter.
However, 「どこですか」 omits the place relationship conveyed by 「で/に」. When the verb must remain, the appropriate particle must still be selected.
- Example: トイレはどこですか。
Kana: トイレはどこですか。
Translation: Where is the restroom?
This is extremely common in actual travel conversation; there is no need to say the full 「どこにありますか」 every time. - Example: 朝食はどこですか。
Kana: ちょうしょくはどこですか。
Translation: Where is breakfast?
With clear context, this can ask for the breakfast location. To ask explicitly where breakfast can be eaten, 「朝食はどこで食べられますか」 contains more information. - Example: イベント会場はどこですか。
Kana: イベントかいじょうはどこですか。
Translation: Where is the event venue?
This seeks the venue’s location. To ask where the event itself will be held, use 「イベントはどこでありますか」.
▌Choosing 「どこで/どこに/どこですか」 in the Same Situation: Each Retains Different Information
「どこですか」 is not simply 「どこで/どこに」 with a particle exchanged. 「どこで」 and 「どこに」 retain a verb and clearly state the type of place relationship being asked about. 「どこですか」 omits that layer and directly asks where an object or place is. 「〜はどこですか」 is common when looking for restrooms, counters, stations, and other facilities. When asking where to eat, buy a ticket, or hold an event, retaining 「どこで+verb」 is usually clearer.
- Example: トイレはどこにありますか。
Kana: トイレはどこにありますか。
Translation: Where is the restroom?
The sentence fully states where the restroom exists; 「どこに」 and 「あります」 together mark the facility’s location. - Example: トイレはどこですか。
Kana: トイレはどこですか。
Translation: Where is the restroom?
This is shorter and natural when asking directions. Because 「トイレ」 is itself the facility being sought, the listener understands the location question even without 「にありますか」. - Example: 朝食はどこで食べられますか。
Kana: ちょうしょくはどこでたべられますか。
Translation: Where can I eat breakfast?
In a hotel, 「朝食はどこですか」 may also be understood as asking for the breakfast location, but 「どこで食べられますか」 explicitly asks where the action of eating breakfast is possible and is more complete.
Practical Japanese 「どこで/どこに」 for Travel: Facilities, Meals, and Events
Both 「どこで」 and 「どこに」 frequently appear during travel in Japan. When looking for a restroom, locker, or service center, the question concerns a facility’s location and uses 「どこに」. Asking where to eat breakfast, buy a ticket, or exchange a ticket concerns an action site and uses 「どこで」.
Event information adds another layer. To locate the “venue” itself, use 「どこにありますか」. To ask where fireworks, a festival, or a performance will occur, use 「どこで」.
▌Situation ①|Asking About Breakfast at a Hotel Front Desk
A:朝食はどこで食べられますか。
ちょうしょくはどこでたべられますか。
Where can I eat breakfast?
B:二階のレストランでお召し上がりいただけます。
にかいのレストランでおめしあがりいただけます。
You can enjoy it at the restaurant on the second floor.
📌 Grammar Point: 「食べる」 is an action, so 「どこで」 asks where breakfast can be eaten. The answer likewise uses 「レストランで」.
▌Situation ②|Finding the Lost-and-Found Center at a Station
A:忘れ物センターはどこにありますか。
わすれものセンターはどこにありますか。
Where is the lost-and-found center?
B:改札を出て、右側にあります。
かいさつをでて、みぎがわにあります。
After you exit the ticket gate, it is on the right.
📌 Grammar Point: 「忘れ物センター」 is an existing facility, and the question seeks its location, so it uses 「どこにありますか」.
▌Situation ③|Asking About a Fireworks Festival at a Tourist Information Center
A:今日の花火大会はどこで行われますか。
きょうのはなびたいかいはどこでおこなわれますか。
Where will today’s fireworks festival be held?
B:川沿いの公園で行われます。
かわぞいのこうえんでおこなわれます。
It will be held at a riverside park.
📌 Grammar Point: A fireworks festival is an activity and the park is where it occurs, so 「で」 is used. Changing the question to 「花火大会の会場はどこにありますか」 shifts the focus to the venue’s location.
Cultural Notes:
- At Japanese stations, department stores, and tourist facilities, 「〜はどこですか」 is often used directly to ask for a location. 「コインロッカーはどこですか」 is already fully natural. 「どこにありますか」 carries more information but does not need to be said in full every time.
- Event information often contains both 「場所でイベントがあります」 and 「場所で開催されます」. The former is a common beginner pattern; the latter more clearly expresses “being held” in notices, event websites, and formal questions.
- 「に」 does not only mark place. In 「友達に会う」, it marks the person met; in 「七時に会う」, it marks time. Always check the relationship between the preceding noun and following verb.
Comparing Japanese 「どこで/どこに」 with Korean 「어디에서/어디에」
Korean 「어디에서」 is close to Japanese 「どこで」 and mainly asks where an action or event occurs. Korean 「어디에」 resembles 「どこに」 and commonly marks an existing location or destination.
The two languages divide this pair of place particles quite similarly. Once “action site” is separated from “existence/destination,” the forms can be compared directly. Even so, the Chinese word 「在」 cannot always be mapped to one fixed particle.
◆ Similar Grammar: Korean 「어디에서」 Corresponding to 「どこで」
Korean 「어디에서」 asks in which place an action is performed and closely resembles Japanese 「どこで」. Concrete actions such as eating, shopping, working, and studying can be compared with this pair.
- Example: 어디에서 점심을 먹어요?
Romanization: eo-di-e-seo jeom-sim-eul meo-geo-yo?
Translation: Where do you eat lunch?
「먹다」 is the action of eating, and 「어디에서」 asks where it occurs, corresponding to Japanese 「どこで昼ご飯を食べますか」. - Example: 어디에서 이 가방을 샀어요?
Romanization: eo-di-e-seo i ga-bang-eul sa-sseo-yo?
Translation: Where did you buy this bag?
「사다」 means buying. 「어디에서」 asks where the purchase took place, just as Japanese says 「このかばんはどこで買いましたか」. - Example: 주말에는 어디에서 공부해요?
Romanization: ju-mal-e-neun eo-di-e-seo gong-bu-hae-yo?
Translation: Where do you study on weekends?
「공부하다」 is an activity performed somewhere, so it uses 「어디에서」 and corresponds to 「週末はどこで勉強しますか」.
◆ Similar Grammar: Korean 「어디에」 Corresponding to 「どこに」
When Korean 「있다」 indicates that someone or something exists somewhere, the place takes 「에」. 「어디에 있어요?」 therefore closely resembles Japanese 「どこにありますか/いますか」.
- Example: 화장실은 어디에 있어요?
Romanization: hwa-jang-sil-eun eo-di-e i-sseo-yo?
Translation: Where is the restroom?
A restroom is a facility that exists at a location, so 「어디에」 is used, corresponding to 「トイレはどこにありますか」. - Example: 지금 민수 씨는 어디에 있어요?
Romanization: ji-geum min-su ssi-neun eo-di-e i-sseo-yo?
Translation: Where is Minsu now?
The sentence asks a person’s location. 「어디에 있다」 corresponds to Japanese 「どこにいますか」 for personal existence. - Example: 호텔은 어디에 있어요?
Romanization: ho-tel-eun eo-di-e i-sseo-yo?
Translation: Where is the hotel?
The hotel is an existing place, and the question seeks its location, so it uses 「에」, like 「ホテルはどこにありますか」.
◆ Similar Grammar: Korean 「어디에」 Corresponding to Destination 「どこに」
Before movement verbs such as 「가다」「오다」, Korean 「에」 marks a destination and closely resembles Japanese 「に」 before 「行く」「来る」. The question is not where an action occurs but where the movement ends.
- Example: 주말에 어디에 가요?
Romanization: ju-mal-e eo-di-e ga-yo?
Translation: Where are you going this weekend?
「어디에」 asks for the destination of 「가다」 and directly corresponds to 「週末はどこに行きますか」. - Example: 이제 어디에 가요?
Romanization: i-je eo-di-e ga-yo?
Translation: Where are you going now?
The sentence confirms the next destination, so it uses destination 「에」; Japanese can say 「これからどこに行きますか」. - Example: 공항에서 어디에 가요?
Romanization: gong-hang-e-seo eo-di-e ga-yo?
Translation: Where are you going from the airport?
Both 「에서」 and 「에」 appear. 「공항에서」 marks the starting point and 「어디에」 asks the final destination, corresponding to 「空港からどこに行きますか」.
◆ Core Difference from Japanese 「どこで/どこに」:
Japanese 「で/に」 and Korean 「에서/에」 are quite close in their basic place functions. 「カフェで勉強する/카페에서 공부하다」 both mark an action site, while 「東京に住む/도쿄에 살다」 both mark residence. Activities and events also often use 「で/에서」 for their site; 「公園で祭りがあります」 corresponds to 「공원에서 축제가 열려요」.
「どこで」 and 「どこに」 are confusing mainly because Chinese does not divide these place relationships so finely. The same restaurant supports both 「レストランで食べます」 and 「レストランにいます」. The first says where eating occurs; the second only says where a person currently is. Although the place is identical, the particle follows what the sentence expresses.
Use the same method with 「あります」. Restrooms, ATMs, and convenience stores exist at a position and use 「に」; festivals, games, and meetings occur at a place and use 「で」. When travelers only need to find a restroom, counter, or station quickly, 「〜はどこですか」 is enough. When the verb must be stated, decide whether the question concerns “where something happens” or “where a person, thing, or destination is.”
FAQs
「どこで」 mainly asks where an action or event occurs. 「どこに」 mainly asks where a person or thing is or where movement is headed. 「どこで食べますか」 asks for an eating location, 「トイレはどこにありますか」 asks for the restroom’s position, and 「どこに行きますか」 asks for a destination. Checking the following verb is more accurate than translating both directly as “where.”
An ordinary question about residence uses 「どこに住んでいますか」. 「住む」 treats the place as a point of living and remaining, so it uses 「に」. 「で」 appears for an activity performed in the place of residence, as in 「東京で働いています」 or 「大阪で勉強しています」.
Both are natural and mean “Where are you going?” 「に」 more readily treats the destination as the final endpoint, while 「へ」 preserves a slight sense of proceeding in a direction. With basic movement verbs such as 「行く、来る、帰る」, both can usually be used, so the nuance need not be overstated.
Both are natural. 「トイレはどこですか」 is shorter and extremely common at stations, restaurants, hotels, and other travel settings. 「トイレはどこにありますか」 fully states that the facility’s existing location is being asked about. A quick request for directions does not need to be lengthened merely for completeness.
「あります」 can indicate either the existence of an object or facility or the occurrence of an activity or event. 「銀行は駅の前にあります」 uses 「に」 for the bank’s location, while 「駅前でイベントがあります」 uses 「で」 because the event occurs in front of the station. Decide whether the subject is an “existing thing” or an “occurring event.”