Being asked a question you cannot answer yet sounds like a waste of time. Research on pretesting suggests the opposite: an unsuccessful attempt to answer can make the answer, when it arrives, stick better.
The pretesting effect
Richland, Kornell and Kao (2009) had students read an essay about vision. Some first tried to answer questions about concepts in the essay before reading it; others simply spent that time reading. Across five experiments, the students who were pretested did better on a later test, even on the very questions they had got wrong on the pretest.
A likely explanation is that a question prepares the mind for its answer. Having searched for it, you notice it when it appears, and you connect it to what you already tried.