1. Which country's flag is this?
1-1. This is America's flag.
1-2. This is an American flag.
2. Which country use this national flag?
2-1. Japan does.
2-2. Japan use it.
2-3. Japan.
3. In which country is this flag used?
3-1. In France.
(Are the questions and answers all correct? Do you have better questions related to national flags?)
All are fine except 2 and 2-2. In both of those sentences the verb needs to be in 3rd person singular form: "uses."
The answers provided for the given questions are correct. However, there are different ways to formulate the questions to address national flags. Here are some examples of alternative questions related to national flags:
1. Which country does this flag belong to?
2. Which nation's flag is depicted here?
3. Identify the country associated with this flag.
4. Whose flag is this?
5. To which country does this flag pertain?
6. Name the nation represented by this flag.
Feel free to ask further questions or provide more specific topics related to national flags.