blogger i need some advises

Hello
i have an ebook library blog , what kind of CJ ads choose ?
best regards

Check amazon ebook I guess it will convert better then cj.

CJ is probably not the best choice. If you're in the eBook market, you're probably better off on Clickbank. Or, Ryan Deiss had a "make money publishing on Kindle" offer that converted really well that you might want to look into. By and large Commission Junction targets a pretty different market than the eBook market.