There are two simple ways to view a user's completion inside of Trainual. The first is by simply viewing their profile page to see their completion on everything they are assigned. You can do this by clicking "Users" in the left side navigation, and then clicking their name. This page will show you all of the user's assigned Subjects, along with their completion of each.
The second way to view all users' progress of a particular Subject would be within the Reports section of Trainual. Navigate to "Reports" in the left side navigation. Find the Subject that you're interested in, and then click "By User" in the top right side. That will show you every user who is assigned that Subject, along with their completion of the Subject.