잖아(요) means 'You know ___/You know it's ___' 잖아요? means 'Don't you know ____?' Example (1) - Someone telephones their friend early Sunday morning. Friend complains, 오늘은 일요일이잖아요? - Don't you know it's Sunday? Example (2) - Someone asks if their friend wants to visit Japan. Friend answers, 나는 돈이 없잖아요 - You know I've got no money. The 잖아요 ending is basically saying "isn't it?" Check here ! :D http://koreanwikiproject.com/wiki/index.php?title=%EC%9E%96%EC%95%84%EC%9A%94