How do you ask: "What's happening?" in Spanish?
Well, in Mexico, if you see a friend you haven't seen in a while instead of saying "¿Qué pasa?" (what's happening) you say, "¿Qué pasó?" (What happened?) As in, what's happened since I saw you last?
I think this is a question with probably a thousand answers. Growing up in Los Angeles, I always heard ¿Qué pasó? But I'm sure there are a lot more, just like in English there are a lot of ways to say the same general thing.