My approach:
-Skim the explanations of ALL questions - even the ones you get correct
-If something is completely unfamiliar, I find that topic in FA and see if that fact, concept, etc. is in FA. If it is, then I highlight it and read about that disease, pathway, etc. If it isn't, I annotate FA with what I think is the important info to know
Keep in mind that many question explanations (Kaplan included) have a lot of ridiculous details that, IMO, aren't worth learning. What those things are is up to you and your goals. Also, from personal experience with the Kaplan Qbank, it tends to be very detailed and test/explain very random and relatively unimportant concepts. Keep that in mind as you work through it.