1. Which country's flag is this?

Question

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?)

Answer 1

All are fine except 2 and 2-2. In both of those sentences the verb needs to be in 3rd person singular form: "uses."