잘 모르겠어요 means “I don’t really know” or “I’m not sure.” It is a polite way to express uncertainty or lack of knowledge about a topic.
Literally it means
good not-know-likely – it seems I’m good in not knowing it 😉
Uses of 잘 모르겠어요
When unsure about something
A: 이 문제의 답을 아세요? (Do you know the answer to this question?)
B: 잘 모르겠어요. (I’m not sure.)
When needing clarification
A: 이 설명 이해했어요? (Did you understand this explanation?)
B: 잘 모르겠어요. 조금 더 설명해 주세요. (I’m not sure. Please explain a bit more.)
Politely expressing doubt
A: 내일 날씨가 어떨까요? (What do you think the weather will be like tomorrow?)
B: 잘 모르겠어요. 뉴스에서 확인해 볼게요. (I’m not sure. I’ll check the news.)
See 모르다