We use "which" as a determiner to ask a question about a specific group of people or things:
我們用限定詞“which”問特定的一組人或物：

Which restaurant did you go to?

Which countries in South America have you visited?

When we are asking a general question we use "what" as a determiner:
用“what”問較為普遍的問題：

What films do you like?

What university did you go to?