내가 얼마나 기다렸는지 알아?

The line, explained

You already know how to ask a plain question: 알아? means 'do you know?'. But real conversation keeps wanting to ask about something bigger: do you know where he went, do you know how much it hurt, do you know whether she's coming. Korean handles all of these with one tidy ending, -는지, which lets a whole question sit inside another sentence. Today's line is a film classic of the type, the one a character says when the waiting is finally over.

Start with 내가, 'I' as the subject. The plain word for I is 나, and when the subject marker 가 attaches, the pair becomes 내가. Next comes 얼마나, a question word meaning 'how much' or 'how long'. On its own, 얼마나 기다렸어? would be a direct question: how long did you wait? In our line, though, the speaker is not asking for a number. They are building up to something, and the ending is what changes the job of the whole clause.

기다렸는지 is 기다리다, 'to wait', in the past tense 기다렸-, plus -는지. Say it out loud and the double ㅆ in the past tense softens into an ㄴ before the next ㄴ, so you hear gi-da-ryeon-neun-ji rather than a hard t sound. That melting is normal Korean pronunciation, not slang. The chunk 얼마나 기다렸는지 now means 'how long I waited', a little question folded up and ready to be placed inside a bigger one.

The bigger one is 알아?, from 알다, 'to know'. Casual present, rising intonation: 'do you know?'. Put it together and you get 'Do you know how long I waited?'. The rule for attaching is simple. Verbs take -는지 in the present (가는지, 오는지) and every stem takes -는지 after the past marker (갔는지, 왔는지). Adjectives in the present use -(으)ㄴ지 instead: 바쁜지 (whether someone is busy), 좋은지 (whether it's good).

Swap the verb and the scene shifts: 내가 얼마나 울었는지 알아? (do you know how much I cried?), 내가 얼마나 찾았는지 알아? (do you know how hard I looked for you?). Change 알아 to 몰라 and you get the even more dramatic 내가 얼마나 기다렸는지 몰라, 'you have no idea how long I waited'. Drop the question word and -는지 means 'whether': 그가 오는지 알아? is 'do you know if he's coming?'. One ending, a whole family of questions.