In the movie National Treasure: Book of Secrets, at the end and in between, the President asks Ben a favor, something which was mentioned in Page 47 in the President's Book of Secrets.
Does anybody know what could be in Page 47?
It is currently unknown. According to the film's FAQ on IMDb:
However, since National Treasure 3 appears to be in production now, this could always be revealed there or at least referenced, despite Turteltaub's assertion.