To access the Audit Log report you can either type "Audit Log" in the global search box or you can press the Reports drop down and select "All Reports". Click on "System" on the left hand side to see the Audit Log.
Change the "View changes" selector to "Events".
In most cases, you will not be searching for changes made to a specific event, but if you are, this ID can be found in the web URL when viewing the event.
If you would like to see any changes made by a specific user, you can enter in their employee ID.
Enter in a valid start and end time to view any changes made.
In my example below, I created a couple new events and edited their start times.
