When Klingon is written in alphabetic pIqaD, there is a triangle symbol with one of the points pointing down that seems to be used much like a comma. In English you can find very strict rules for commas, but, in Klingon, the rules are much less strict and the down pointing triangles seem to mostly be used when they can aid in clarification. In our Roman writing, sometimes this down pointing triangle is represented by a semicolon instead. Similarly, there is an up pointing triangle that is sometimes used to mark the end of a sentence in much the same way we use periods, question marks, and exclamation points.
No, it cannot.
nuqjatlh? is not a complete sentence with a proper verb in it -- it's just an interjection, a reaction to something somebody said or is saying that you can't understand.
"Huh? What? Eh? What was that? What did you say?"
You can't react like that to something the person has not said yet.
On the other hand, nuq Dajatlh? can mean "what did you say?", "what do you say?", or "what will you say?" -- that's a proper sentence and not a "Huh?"-style interjection.