Could you please reply to me at your earliest convenience?

가능한 한 빨리 답변을 주시겠어요?

• Would you mind replying to me when you get a chance?
• Probably best to make your decision sooner rather than later.
• your prompt support would be highly appreciated.
• I would be grateful if you could work on this issue immediately.
• I would be happy if you could work on this issue straight away.