RAFO is the common acronym used for saying Read and Find Out. It is used with the implication that the particular question or plot-line for what one wants the answer to, will be revealed in the next, or in a future, book. It is most commonly used for a literary series. The equivalent for the TV series series is WAFO 
(Watch and Find Out).
"Read And Find Out. I have grown so used to that answer, that when my wife asks me if I want to go out for dinner this evening, I sometimes say "Read and find out." That's usually when she hits me."
—Robert Jordan, Source:Scifi.com chat, 1 November 1998
—Robert Jordan, Source:Scifi.com chat, 1 November 1998