Currently, when a teacher sets a quiz to "lock questions after answering" (meaning that the student cannot go back and change an answer to a question as they progress through the quiz), there is no confirmation pop-up asking if the student really wants to submit their answer before going to the next question. Although there is one at the end of the exam, this does not do any good if the exam is set up such that individual answers are submitted.
Case in point: During an exam today, one of our questions was an essay question. Half-way through answering the question, I decided to try and format my answer some. I went to the top of the paragraph and tried to put in an indentation. Unfortunately, in my test-induced foggy mind, I tried to do this by hitting "Tab." This automatically moves my cursor to the "Next" button (indicating that I would like to submit my answer and move on to the next question). I had not noticed this though, and upon seeing that the paragraph was not indented, hit the space bar in order to do a manual indentation. Sadly, by hitting the space bar, this indicated to canvas that I hit the next button and my answer was submitted before I had finished answering the question. This could have been avoided if a pop-up box had been triggered after hitting "next" that asked if I was certain that I wanted to submit my answer (like it does at the end of the test).