If the teacher asks the students after the class, Do you have any questions? <-- added a couple of "s"s What is the best response from a student? <-- Capital, reponse, question mark " No. It's quite clear. <-- added full stop and apostrophe (Good) No. It's already clear. No. I think it's enough --> No. I think I have enough to work it out. <-- something like this? No. So far so good. (Good)

The first answer is excellent. The fourth answer is also excellent, but informal. The second answer is very slightly impolite, because it implies that the teacher might be boringly repetitious. The third answer doesn't make sense in the context.

These four responses are proper to answer that question.