If one really and truly has NO clue, then one skips the question and goes on. It's rarely the case that one has NO clue, however: for the author one has never heard of, one draws on one's knowledge of the period and style, and if one can't draw on one's knowledge of the period and the style because one never heard of THEM before, one considers the label that said period or style is given and figures out what it must mean and what it can't mean. (For instance, "postcolonial" isn't going to refer to the US, because the US went straight from colony to independent nation, so the place in question is most probably some place in which European nations had colonized earlier but are no longer colonial powers, which makes the period post-World War II.)
Education isn't what you know. It's what you can do (and fake, intelligently) with what you know.