From inside your Brightspace course, select the "Course Menu" drop down menu, then select the "Discussions" button

On the Discussions page, navigate to the discussion that has been graded, select the discussion.

The "View Topic" page opens for the selected discussion. Once the instructor has graded the discussion and provided feedback, the "Feedback" section will display the instructor's comments. You can also select "View Graded Rubric" to see your grades based on the rubric used for the assessment.