If jokes or ancient fables are used in the novel, is it plagiarism?

You can do it with confidence. This kind of quotation is not plagiarism, but it usually indicates the source. For example, there is a story in Shan Hai Jing. Of course, sometimes you don't have to say the source;

This is very common in literary creation.

Even the most plagiarized papers are cited. Therefore, plagiarism of a certain paper mainly means that the viewpoint is the same as most of the length. Writing should be meaningful. If you want to express the views and statements that others have already said, if you copy mechanically and have nothing new, you will be accused of plagiarism. Like a citation in a paper, it usually indicates the article from a book, or what version of a book and how many pages.

This is respect for the original author, so the quotation is only for further demonstration on the basis of the original author.