About the question So, by 'type of questions', I really mean this from an ontological perspective. I imagine there is a complete set of (type of) questions, and thus any question that ever was or will be asked will be of one type or the other belonging to such a set.
A problem In trying to form such a set containing all question types, is there a way we could know for sure that we have covered all possibilities? Say we never had a concept of time, we could thus never ask 'when' something happened. Furthermore, if this was the case, it's not like we could just conclude 'oh, we must be missing the concept of time!', because obviously we would have started with such a concept to make that conclusion to begin with.
My attempt at an answer In trying to derive an answer myself, I have come up with 6 types. These are: when and where (relating to spacetime), what and who (identification and personhood i.e human identification), why (motive) and how (causality).
A problem with the answer It seems as if though however, that many questions can be rephrased to give the same meaning, but using different question types. For e.g, 'how does a ball drop to the earth' vs 'why does a ball drop to the earth'. The answer to both seems to be gravity. So there seems to be a problem of interchangeability. Now I know that why and how aren't always interchangeable, such as 'how did he murder' vs 'why did he murder', but when they are, that seems to be problematic.
Summary So, how can we go about forming the set of all question types, and can we know when we have done so? Furthermore, why is it that some question types seem interchangeable when such types are of a different nature to each other? Maybe it's just a matter linguistic confusion?