To see the courses you've already completed, first navigate to the Training tab. This can be found by clicking Training in the menu on the left-hand side of the screen on the Web app, or by clicking the open book icon at the bottom of the screen in the Mobile app.
On the Training screen, you can toggle between the courses you've already completed and the courses you still have to complete, by using the To Do and Completed buttons at the top of the screen.
When you click Completed, this will show you the Learning Tracks you've completed all courses for. Click anywhere on the box with the name of the Learning Track to see the individual courses in that track. This will show you a list of completed courses in that Learning Track, as well as how long ago you completed them.
If you can't find a completed assignment, it could be that a Company Admin archived the content. Reach out to your Company Admin, or contact us here on the support site or at firstname.lastname@example.org.