As an Observer, you can always check the grades for your observed students/enrollments even if that enrollment is completed.
1. Select the student you wish to view the grades for.
2. You will see the course titles for any current courses they are enrolled in.
3. Click on the hamburger menu (3 bars) in the upper left
4. Click on Grades
5. You will now see the grades for the user's current courses.
6. Click on Past Courses in the bottom left
7. This screen will show any previous grades they may have.