To monitor a user's activity, first go to the "Users" tab on the left side of the page. Select any user from the list of users in your account.
In the user's profile, you can see their overall completion percentage for all assigned Subjects. The completion percentage is based on completion at the Topic level, so the percentage will automatically increase as a user completions Topics that are part of assigned Subjects.
To see a user's recent activity, click on the "Recent Activity" tab at the top of the page.