For the AP US History exam, what should I do if I don't know the answer to an essay question?

I just took the final (not the AP exam) and this happened to me. Luckily, I got some info on the subject through the multiple choice. I bs-ed my way through it with a skimpy 4 paragraphs. Just repeat lecture and write as much as you can about the little details you do know. Or do something like I did and just change the subject. You'll at least get a 2 if it's relevant. Better than a 1 I guess. For example, "Analyze George Washington's policies and motives during his presidency." I would write "George Washington is a courageous leader who refused to take the crown. His perseverance is admirable. His policies were amazing and helped his citizen immensely. George Washington is comparable to FDR who..." That's saying that I know a lot about FDR and not GW. I hope this helped. I sound crazy, but it's better than not writing anything. Make sure your thesis is AMAZING. The thesis drives the entire essay and can earn you points even if your essay is crap.

You're talking about during the actual exam, correct? Write down ANY possible thing you THINK MAY be related. The FRQs are the only ones you would have to worry about this happening on. On the DBQ, even if you have no outside information, you would learn from the sources. A beautiful thing about the APUSH exam is that for each FRQ you're given two options. That way if you are unsure of one, you can do the other.