지 모르다

not know what or whether

This is the -(으)ㄹ지 모르다 shape, where the question is left open and 모르다 says you cannot settle it. With a question word it means not knowing which: 우리 내일은 뭐 팔지 몰라요, 그래서 어떻게 돌아가지 모르겠는데. Without one it hedges — 요즘에 안 그랬지 모르겠지만, "though it may not be like that these days" — or reports that something was not expected: 울지 몰랐어. These lines are short fragments of casual speech with no formal use shown.

Register: casual