じゃん: (casual) sentence ending asking for agreement: isn't it?; right?; you know (from じゃない)

「スーツ、似合にあってるじゃん。」「馬子にも衣装まごにもいしょうって言いいたいんだろ？」

"That suit looks good on you." "You mean fine clothes make anyone look good, right?"