To access the Session Attendance Report, navigate to reports then "Session Attendance".
Use the Cog to select Attendance Report Settings:
Count In Progress Sessions
Count Substituted Exercises As Completed
Exclude Volume from Exercises with no Planned Load
Use the Measure drop-down menu to select the data you want to view:
Sessions: Assigned Sessions, Completed Sessions, and Session Completion Percentage
Exercises: Assigned Exercises, Completed Exercises, and Exercise Completion Percentage
Sets: Assigned Sets, Completed Sets, and Set Completion Percentage
Volume: Assigned Volume, Completed Volume, and Volume Completion Percentage
You can also filter the report by athletes, groups and the programs selected by using the drop downs as well as specifying the date range.