nuqjatlh is a special word that stands alone as its own sentence, an exclamation. It is not simply a short form of the sentence nuq jatlhWhat did he/she say? You could not, for instance, say nuqjatlh HoDWhat did the captain say?
It would be a fine thing to say in that situation. It means, "I do not understand it." However, the English you are being asked to translate here is just, "I do not understand," which would be equally to, jIyajbe'.