(Warning: I'm still learning, not a native speaker)
Где would be used when asking where something CURRENTLY IS, but you would use куда when asking where someone (maybe something? not sure about that) is GOING. (didn't know how to italicize through comments on the question, so caps it is!) If I'm wrong, please someone say so...
When we talk about going as a repeated action, we use the verb ходить, not идти. So the question would be "Куда ты ходишь?". Here are some good explanations: http://www.russianforeveryone.com/Rufe/Lessons/Course1/Grammar/GramUnit15/GramUnit15_1.htm http://masterrussian.com/verbs/verbs_of_motion.htm