What are the different ways to say "why, what, where, who " in Korean?

Question

I want to learn the different ways to say what, where, why, and who. I know that for settings, formality, subjects, and other topics, These words can change a little bit, so I want to know more words that are or is related to it. I already got some words like 뭐,무슨,어떤, and 몇.

Answer 1

To make it not too long, here are variants and related phrases of "what".

• 무엇: original pronoun for "what". 1) what (question word), 2) "something" in non-question contexts.
  뭣, 무어, and 뭐 are shortened forms used in speech.

   생일 선물로 무엇이/뭣이 좋을까? / 뭐가 좋을까? (subjective case) = What birthday present would be good?
   생일 선물로 무엇을/뭣을 사 줄까? / 뭐를/뭘 사 줄까? (objective case; 뭐를 contracts to 뭘) = What birthday present should (we) buy?
   무엇이라고? / 뭣이라고? / 무어라고? / 뭐라고? = What (did you say)? 
   무엇/뭣(을)/뭐(를)/뭘 좀 먹자 = Let's have something to eat.
  

• 무슨: determiner form modifying a noun. 1) what, 2) "some/any kind of" in non-question contexts.
  뭔 is its informal shortened form (it sounds a bit sloppy/slurred though).

   무슨/뭔 일이야? = What's going on?
   무슨/뭔 이유가 있겠지. = There must be some reason.
  

Related words:

• 어떤 (short for 어떠한): 1) what kind of, 2) a certain/some/any kind of

   어떤 영화를 좋아하세요? = What kind of movies do you like?
   어떤 영화도 다 좋아해요. = I like any kind of movies.
   어떤 사람이 찾아왔어요. = A certain man has visited us.
  

• 웬: shortened form of 어찌된 or 무슨 or 어떠한/어떤. It asks the background usually expressing unexpectedness rather than what it is.

   이게 웬 일이냐? = What in the world is this? (asks how it came to be so)
   웬 비가 이렇게 많이 오냐? = 무슨 비가 이렇게 많이 오냐? = What's with this heavy rain?
  

(몇 is "how many" or "a few", so it is not directly related to 뭐 or 무슨)