Moodle has tons of reports available for the Site Administrator and for the Teachers as well. If Activity completion is enabled by the administrator and in the course settings, teachers can indicate for each course item how they wish it to be registered as complete. A tick/ checkmark will then appear against the activity. Students may either mark it complete manually or the item will automatically be registered as complete once a student has met the specified criteria.
To check on who did not participate in the course:
Step 1: Go to your course page
Step 2: Click on the Report tab from the secondary header menu
Step 3: Click on the 'Activity Completion' report. The list of students and their activities should be displayed. A tick/ checkmark will appear inline of the activity that is already completed by the student.