Students can only skip questions in custom tasks, where the teacher has chosen the questions and which order. Students can click the progress bar along the top of their workbook to skip a question. At any time they can click back where there is a gap.
We don't have a skip question button for adaptive tasks as we want students to get a full worked example by using the hints and next steps. That way, when students see a similar question later they can show that they have learned from the previous question and apply their new knowledge.