The student activity report is available via the Analytics button (to see these options, click Course Home and then select an assignment on the Assignments tab of the course home page):

The student activity report shows various statistics about each individual student's engagement with a particular assignment:

• How much time the student had the reading assignment open*
• How much time the student was reading actively (some sort of mouse movement or keypress at least once every ~2 minutes)*
• How many comments the student submitted
• How many times the student "upvoted" another student's question or comment (by clicking the button indicating they have the same question, or click the button indicating that a particular comment was helpful for their understanding)

* Because students can access a particular page of reading either through an assignment or by opening the whole book directly (through the Document Library), the timed reading statistics are counted only when students access the assignment directly by opening the assignment in the Upcoming or Past Assignments panel. Reading that occurs when the student opens the full book or document through the Document Library will not be counted here.