Яка means "what /which" unlike що which just means "what." From what I know яка is more appropriate for sentences where you can apply "which." Which is the next stop ( A or B)? Which ice cream do you like? Що is more appropriate for where "which" wouldn't work. "What are you doing? What do you want to do tonight?" Also the form of this word is determined by gender. Який (m) Яка (f) and Яке (n). I'm guessing that a more accurate translation of this sentence would be "Do you know which is the next stop?"
I've noticed that in the examples (sentences) given in this thread, що (and "what" as its translation) relates to the verb (Що ти робиш? What are you doing?), whereas який relates to nouns (яка наступна зупінка? What stop?).
I don't know if this applies always (and also, the sentences with яка/what might be complicated by the fact that there is (or is omitted, in case of Ukrainian) a copula), but maybe it is a way to go.
And I'm really sorry if my comment is not very helpful / understandable - I used to study Linguistics and couldn't help posting this :)