Student or Learner
What a knob / nob!
Which one is correct? they sound exactly the same!
It depends on what you want to say.
A knob used in this manner is not a door knob, rather it is slang for an obnoxious person (in Canadian English this is certainly true and I think it is so in American English too.)
A nob is also slang for a person of wealth or high social position (probably British English)
So which one is correct? They both are and depend on the person who says the sentence.