From Wiktionary, the free dictionary
Contraction of 지 않아 (-ji ana).
잖아 • (-jana)
- (used with verbs) Used to emphasize some statement is correct.
- 그리고 너 그거 알잖아. ― Geurigo neo geugeo aljana. ― And you know it.
- (used with verbs) Used to contradict previous statement is indeed correct.
