Formal:
* നിങ്ങൾ എന്തു ചെയ്യുന്നു? (ningal enthu cheyyunnu?) - This is the most formal way to ask.
* നിങ്ങൾ എന്ത് ചെയ്യുകയാണ്? (ningal entha cheyyukaayanu?) - This is another formal option.
Informal:
* എന്താ ചെയ്യുന്നേ? (entha cheyyunne?) - This is the most common informal way to ask.
* എന്താ ചെയ്യുകയാ? (entha cheyyukaaya?) - This is another informal option.
For friends/family:
* എന്താ പണി? (entha pani?) - This literally translates to "what's the work?", and is a very casual way to ask.
The best way to choose the right phrase depends on who you are talking to and the situation.