Formal:
* आप क्या कर रहे हैं? (aap kya kar rahe hain?) - This is the most formal way to ask. It literally translates to "what are you doing?".
* आप क्या कर रहे हैं? (aap kya kar rahi hain?) - This is the formal way to ask a woman.
Informal:
* क्या कर रहे हो? (kya kar rahe ho?) - This is a more casual way to ask, suitable for friends or family.
* क्या कर रही हो? (kya kar rahi ho?) - This is the informal way to ask a woman.
* क्या चल रहा है? (kya chal raha hai?) - This is a more casual way to ask, meaning "what's going on?". It's more suitable for friends.
* क्या चल रही है? (kya chal rahi hai?) - This is the informal way to ask a woman.
You can also ask more specifically about what someone is doing:
* क्या आप काम कर रहे हैं? (kya aap kaam kar rahe hain?) - Are you working?
* क्या आप खाना खा रहे हैं? (kya aap khana kha rahe hain?) - Are you eating?
* क्या आप पढ़ रहे हैं? (kya aap padh rahe hain?) - Are you studying?
Remember to use the appropriate form of the verb "करना" (karnaa) based on the gender of the person you are talking to.