Explanation
-냐? is the plain-speech question ending, the question half of 반말체. Attach -냐? to any stem in everyday speech (가다 → 가냐?, 먹다 → 먹냐?, 예쁘다 → 예쁘냐?); the fuller -느냐? after action verbs (먹느냐?) sounds literary or old-fashioned. It is curt and only for close friends, juniors or talking to yourself; the softer plain question is -니?. 지금 뭐 하냐? — What are you doing right now?