quiz comments are not saved

Which commends do you mean?

I don’t understand. The quiz has no comments.
If you mean the comments in the post itself, they can be seen in the main WP Comments page in your dashboard.

This is just an open-end question. You can see its answer along with all other answers in Quizzes -> View Results -> Details pop-up.
But to see the answers there you have to include the %%ANSWERS%% variable in the final screen of the quiz.