Remove Question from Bank after Answered in Storyline 360

Each draw from a given question bank (QB) randomly selects the designated number of questions. Storyline doesn't have a way to skip questions that were shown in a previous draw. 

You could consider using more QBs. Put fewer questions in each QB, and don't repeat questions. Then draw from the different banks at different points in the course. That would ensure the user doesn't see the same question twice.