잖아

you know / remember, right?

Points at something the speaker assumes the listener already knows or can see for themselves, asking for a nod rather than an answer: 했잖아 'I told you, remember?', 할 수 있잖아 'come on, you know you can do this'. It can also nudge someone toward an obvious conclusion, as in 해냈잖아 'but you did it, didn't you'. 있잖아 at the start of a turn is just 'hey, listen'. All the examples here are casual talk between people who are close; adding 요 (잖아요) makes it polite.

Register: casual; 잖아요 for polite