Student or Learner
This might be a challenge to native English speakers!
In China, we ask "you shen me shi qing ma?" when we realize that someone might in need of any help. This sentense could be roughly translated into "Do you have any problems that I can help?" This rough translation might doesn't work to most native English speakers. (Perhaps yes, but I really don't know.) Guess "Can I help?" or "Is there anything I can help?" might be the answers. But I just wonder if "What's going on" also relay the same feeling? ("relay the same feeling" might also be wrong. If so, please correct me.) And I'd love to have as many as options for this situation, and if possible detailed analysis on the difference.
To whoever answers this question, "thank you a million"!
In a formal setting, "May I help you?" would be used. Other alternatives: "Can I help you with something?" or "Anything I can help you with?" (even though it ends in a preposition, which is usually frowned upon, it is often used in business situations.)
"What's up?" or "What's going on?" are generally used as a casual greeting to friends. It's a very casual way of asking "How are you?" It can be used in a business setting occasionlly, though; perhaps in an environment that caters to young, trendy, "hip" customers (a music store, a clothing boutique, a tatoo parlor) the sales staff might greet customers with "What's up?" instead of "May I help you?"
I hope this made some sense!