~는지 (verb)
~(으)ㄴ지 (adjective)

whether, if

내일 우리 만날 수 있는지 알고 싶어요 – i want to know whether we can meet tomorrow
너무 맛있었어요! 어떻게 만들었는지 가르쳐 주세요 – It was delicious! Please tell me how you made it.
여자 친구가 있는지 없는지 궁금해요 – I wonder whether he has a girlfriend.|
문제가 있는지 물어보세요 – ask them whether there’s a problem
이거 괜찮은지 봐 주세요 – see if this is okay

whether… or.. (은/는지… 은/는지…)

사기꾼인지 강돈지 – whether he might be a swindler or a burglar

perhaps because

바람에 흔들리는지 -perhaps because they were being shaken by the wind
그래서 그런지 – maybe that’s why
그것도 자기 팔자소간인지 – it may be that this was his fate
만족하는 때문인지 – perhaps it was because of my satisfaction

uncertainty about what/why/when/where

뭐 사고 싶은지 말해 주세요 – tell me what you want to buy 
어떻게나 쫓아다니는지 – and how she’s following me around