The adjective in this case follows the noun. So the sentence is Tom's two interesting books. or better yet would be Tom has two interesting books. It changes the meaning very slightly as the reader may infer that Tom only has two interesting books. But it is a better way of saying this. Never say two tom's interesting books. That is a fragmented sentence and you will be wrong.

I guess The better way to say it is "Tom has two interesting books". It'll make things more clear to the listener.

2 qualifies book's quantity not Tom's or all the sentence, so I think it must be Tom's 'two' insteresting book.

This is my idea! You can understand this phrase as "two intersting books of Tom", Of Tom = Tom's => Tom's two interesting books. What will happen if we write "two Tom's intersting books". Then, we can't define whether "two" is for "Tom" or for "interesting books", By the way, "two Tom" is wrong, it's correct for "two Toms", two + Nplural. Wish it help!