'which' is the word you use to ask something about a thing. like: which music do you prefer? which phone do you have? which country have you been to? the word 'where' tells something about the place of a thing. like: where do you study? where do you like to eat? where did you buy that? you always need a word like 'do' or 'did' to use 'where' in a sentence.

哪 = na = countable, point towards something specific 哪里= na li = to any place, somewhere, area, region, it has ambiguity, not specific Example: 这是一个地方，我早就想访问的。 这是一个地方，我一直想访问的。

where is used to refer to places like this is the school where i work. we can say the same meaning using which: this is the school in which i work. when we want to say a place but we mean it as a thing we can use which this is the house which my uncle built. which is used to refer to things and can be replaced with that this is the bag which i bought yesterday. this is the bag that i bought yesterday.