Is 'nuq' always a question? I notice that 'nuqjatlh' doesn't have the 'a' suffix that usually makes something a question. I mean, can you say 'nuqjatlh' to mean 'that which was said', like in the sentence, "That's what he said."...? Or is that a different prefix?
nuq is a question word. It is ALWAYS a question. Perhaps the question is rhetorical (asked for effect rather than seeking a response), but it is always an actual question. It should never be used as a relative pronoun like in, "That's what he said," or "I know what that is." The -bogh suffix can often be used for that type of thing.
The verbal -'a' suffix turns a statement into a yes/no question. It is NOT equivalent to a question mark. It should never be used with question words.
nuqjatlh is a special word that is classified as an exclamation. It stands on its own with no other words. Think of it as a one-word question that cannot be made part of any other sentence. While you can analyze it as nuq + jatlh, its components do not grammatically come from What did you say? It's more like Say what?