1) "한국말 할줄아는 사람 모르는대..." = (Someone) said that they didn't know you are a person who can speak Korean. 한국말 할 줄 알다 = from ~(으)ㄹ 줄 알다 = to know how to do something.. 한국말 할 줄 아는 사람 = ~는 is added because 알다 is a verb, and because of the ㄹ irregularity, it is dropped when ㄴ is added to it. ~는 is added to allow the verb to modify the noun. So it changes from just a person (사람), to a person that knows how to speak Korean. 모르는대 = ~대 is a colloquial form that is shortened from ~다고 하다 which is used to indicate that someone said something. Since 모르다 is a verb, ~는다고 하다 is shortened to ~는대. 2) 맞긴 한데 = (But) It's right/correct.. (Maybe you said that it will be wrong, but actually in fact it's correct) This one is 맞다 + ~기는/긴 하다 + 는데. ~긴 하다 is a grammar principle that can be used to downplay what you said. Kind of like to sound a bit modest. ~는데 can used at the end of sentences to express that in actual fact it is the opposite of what was said (so you are a bit surprised). 3) 뒤에 뭐가 오냐에 따라 달라. This one is 뒤에 뭐가 오다 + ~냐에 따라 다르다. It is the same as ~는지에 따라 다르다. ~는지 = used to express uncertainty, ~에 따라 = according to, 다르다 = to be different. So.. <clause>는지에 따라 다르다 = to be different as according to <the clause>, which can be translated to "it depends on <the clause>.

First sentence: "한국말 할줄아는 사람 모르는대..." - I don't know anyone who can speak Korean. "한국말" "할/줄" "아는" "사람" 모르는데..." "Korean" "speak" "can" "anyone" "I don't know" Second sentence: "맞긴 한데" - "It does(or it is) but" "맞긴 하"/"ㄴ데" Third sentence: "뒤에 뭐가 오냐에 따라 달라" - It depends on what is following after it. "뒤에" "뭐가" "오냐/에" "따라/달라" (it)"after" "what" "is following" "depends on"