Have you read the humorous stories _ the Panchatantra?
Without knowing if the Panchatantra is a book or a place or a people, I'd go with 'of' although 'in' might work too. 'About' would mean the Panchatantra were the subject of the stories, not the source.
By the way, are you taking a grammar test right now? Doing homework questions? If so, I'll tell you you're not doing yourself any favors by not learning this stuff yourself.