Use the "Add Text" tool or the "Freehand Draw" tool on the toolbar when reviewing a student's submission to write feedback next to individual questions.

These two tools allow you to leave comments next to a student's work.  If a submission contains a lot of writing or text boxes, you can click the box next to "Show student elements" (PRO) to temporarily hide any writing, text boxes or highlights the student added to the assignment.

*Remember: You can also leave a comment that the student will see at the top of the assignment by clicking on "Comment" on the left hand side of the submission.