1) you could use it when you want to remind of something someone has forgotten. maybe when you want to complain. ;) a: 빨리 나가자 (let's leave here quickly) b: 야! 나 아직 먹고 있잖아(hey! im still eating) 2) you could also use it when you want to remind someone of good things. a: 술 먹으러 가자 (let's go for drinks) b: 안돼(no way) 너 내가 평일에 술 안 먹는거 알잖아(you know i dont drink during weekdays) c: 바보(babo). 오늘은 금요일이잖아(today is friday). we dont work tomorrow(우리 내일 일 안해)

the means of "이쟎아' is 'is' but you usally use this '이쟎아' when you have opposing views for example.. there are two guys, A and B A: hey, Let's go to museum B: Today is sunday! (museum is not open today) A: 박물관 가자! B: 오늘은 일요일 이쟎아! A:Hey why didn't you come yesterday, i'was wating for you! B:Our meeting day is today! A: 야. 너외 어제 안왔어, 기다렸쟎아.. B: 우리 만나기로 한날은 오늘 이쟎아!