1. Navigate to the Grade Report by clicking on Grade under the assignment on your homepage, or going to Reports on the navigation bar to the left and selecting the Grade report in the first column. 

2. Open either Grade by Student or Grade by Question tab and click on the plus sign to the left of the student's name. You can then select Add Remarks in the shaded gray bar. 

The student will get a notification via their bell and can see the comments in their Student Report.

Note: If the Hide Answer Details in Report setting is turned on in Assignment Settings, students will not be able to see comments in their Student Report.