If you want to know what book someone is reading now, you would ask "What are you reading at the moment?" or simply "What are you reading?" if they actually have the book in their hand.
As far as your answers go, "I am reading Diary of a Wimpy Kid" means that you have already started reading it and have not yet finished it. "I have been reading Diary of a Wimpy Kid recently" can mean the same thing, although it suggests that you might not be actively reading it, even though you haven't finished it. "I read Diary of a Wimpy Kid recently" means that you have finished it in the recent past.