이거는 한국어가 어느 정도 되야 공부할 수 있는 것 같아. (되야 -> 되어야 or 돼야) = It appears you have to be at a decent level of Korean to be able to study this. = It appears you can only study this if you're at a reasonable level in Korean. 어느 정도 here means "at a certain level" or "in some degree". 어느 and most other questions words in Korean are used both in questions and in declarative statements. When not in a question, these words have the meaning of "a certain", "some", etc. e.g. - 무엇 = what; something, anything. (무엇 좀 먹자 = Let's have something to eat.) - 어떤 = what kind of; some/any kind of. (어떤 사람이 찾아왔다 = Some guy came by). - 어느 = which; some, a certain. (어느 것도 괜찮아요 = Any of them is fine.) - 어떻게 = how; somehow, in some way. (어떻게 해 보자 = Let's try and do something.)