"Are you working?'" may be interpreted in two ways. 1. 지금 일하는 중이야? / 지금 일해? / 지금 일하고 있어? (Are you working (right now)?) 2. 지금 일해? (Do you work?) / 직장이 있어 [있니]? (Do you have a job? Are you employed?) #2 is not as likely between close friends (since they would already know).

"지금 일해?" Or even just "일해?" is fine