I said what for "wo" as suggested, but it was considered wrong, why???
The basic meaning of wo is "where".
The list of hints is global -- it's not tailored to the specific sentence you see except that Duolingo tries to put the most relevant hint at the top. Ones further down may or may not apply to the current sentence. (Though I can't think of sentences off the top of my head where wo translates to "when" or "what".)
Unfortunately, Duolingo can get confused when the same word shows up twice in a sentence but has to be translated differently (e.g. "the child sees the cat" where "the" has to be das once and die once -- it will usually show das as the topmost hint for both of them), or when one of the possible hints occurs elsewhere in the sentence (as here, where "wann" does occur in the correct answer, just not as a translation of wo).
So, the hints can be useful but they're never "suggestions" or "recommendations" -- you still have to know what words mean and use that to evaluate whether a given hint is useful or not. They can jog your memory but they're not good at teaching you anything because they're not reliable enough for that.