The Tamil meaning of "what are you doing" can be expressed in several ways depending on the context and formality. Common translations include:

• [நீ என்ன செய்கிறாய்?](javascript:void(0)) (Nī eṉṉa ceykiṟāy?) - informal
• [நீ என்ன செய்து கொண்டிருக்கிறாய்?](javascript:void(0)) (Nī eṉṉa ceytu koṇṭirukkiṟāy?) - describing ongoing action
• [நீ என்ன பண்ணுற?" ](javascript:void(0)) (Nī eṉṉa paṇṇuṟa?) - colloquial form, informal

The phrase can be tailored with slight variations for politeness and context, but these are the most common ways to say "what are you doing" in Tamil.