After all, obviously: … (rồi) còn gì

Còn gì at the end of a statement means "…, you know that", "…, remember?" or "…, after all". It reminds someone of something they should already know, and it often follows rồi: Em nói với anh rồi còn gì! I told you already! Word for word it asks "what else is there?", as if nothing more needs saying.

There's usually a mild reproach in it: you forgot, you weren't listening, you can't back out now. Đi đi, anh hứa rồi còn gì. Come on, you promised. Said lightly, it's just a friendly nudge: Mình gặp nhau ở đám cưới Lan rồi còn gì. We met at Lan's wedding, remember?

Mà at the end is close, and you'll hear it more often in Saigon: Em nói rồi mà! Mà pushes back when someone doubts you; còn gì points to what the other person already knows. Both are for friends and family. With someone older, còn gì can sound like a telling-off, so a gentle mà after dạ is safer: Dạ, em nói rồi mà.

Don't mix it up with the question Còn gì nữa không?, "Anything else?". With nữa không at the end, it's a real question. And Chứ còn gì nữa! on its own is a strong "Of course!"