How do you say Japanese book in Japanese?

If you mean a Japanese book (as in a book from Japan) you would say "nihon no hon" にほんのほん 日本の本

If you mean a book in Japanese (written in Japanese) than it is "nihon go no hon" にほんごのほん 日本語の本

I know that sounds stupid, but you need to specific. One could technically buy a book in all Japanese that did not come from Japan.