Formal:
* Nee engaa irukku? (நீ எங்க இருக்கு?) - Literally, "Where are you?" This is a polite way to ask what someone is doing, especially if you are talking to someone you don't know well or someone older than you.
* Nee enna panreenga? (நீ என்ன பண்றீங்க?) - "What are you doing?" This is a more formal way to ask what someone is doing.
* Nee enna seiyareenga? (நீ என்ன செய்யறீங்க?) - "What are you doing?" This is another formal way to ask what someone is doing.
Informal:
* Nee enna panra? (நீ என்ன பண்ற?) - "What are you doing?" This is a casual way to ask what someone is doing, used with friends or family.
* Nee enna seiyare? (நீ என்ன செய்யறே?) - "What are you doing?" This is another casual way to ask what someone is doing.
* Nee eppadi irukku? (நீ எப்படி இருக்கு?) - "How are you?" This can be used as a casual way to ask what someone is doing, especially if you haven't seen them in a while.
To ask for an update:
* Eppadi irukku? Enna panra? (எப்படி இருக்கு? என்ன பண்ற?) - "How are you? What are you doing?" This is a common way to ask for an update on someone's life.
The best way to understand the meaning of "what you doing" in Tamil is to consider the context and the relationship between the speaker and the listener.