Anyone? Anything? có … ai / gì … không

In a có … không question, ai, gì, đâu and nào stop meaning "who", "what", "where" and "which", and mean "anyone", "anything", "anywhere" and "any": Anh có muốn uống gì không? Would you like anything to drink? Cuối tuần chị có đi đâu không? Are you going anywhere this weekend? The question word sits where the thing would go, usually after the verb.

When "anyone" is the one doing something, có ai opens the question: Hôm qua có ai gọi cho em không? Did anyone call me yesterday? Nào goes after a noun: Gần đây có quán phở nào ngon không? Is there a good phở place near here?

Answer yes with có and the details, or no with the pattern you know: Dạ, không có ai hết (in Hà Nội, cả).

The frame changes the meaning. Anh muốn uống gì? asks what you'd like; Anh có muốn uống gì không? asks whether you'd like anything at all. It works with chưa too: Em ăn gì chưa? Have you eaten anything yet?

With cũng instead, the same words mean "every": ai cũng biết, everyone knows.