Is wewe really necessary?
No, it's likely to appear when emphasising "you", so for example ...
(Mimi) sipendi XYZ. Wewe hupendi nini?
I don't like XYZ. What don't you like?
so "Unaspendi nini?" isn't correct?
could it also be "hunapendi nini"?
no, here's a guide for how the negative is conjugated:
I wrote :unapenda nini? Why is that wrong?
That means 'what do you like?'