There are several ways to copy an event. They are available through ctrl-drag (on PC) or cmd-drag (on Mac) as well as the right-click context menu.
Copy an event to the same sub-calendar
Option 1: Use the context-menu
Right-click the event and select Copy to, then click the date you want the new event to be on.

Option 2: Ctrl- or cmd-drag and drop
On any of the grid view, ctrl-drag or cmd-drag the event and drop it to the date you want the new event to be on.
Copy an event to any sub-calendar
Option 1: Use the Scheduler view
Change to the Scheduler view, ctrl-drag the event and drop it to the column of the sub-calendar you want the new event to be on. The copied event will be on the same date as the original. Hold down the middle handle at the bottom of the event, drag down to expand the time range without opening the editor to change the ending time.

Option 2: Use the Timeline view
Change to the Timeline view, ctrl-drag or cmd-drag the event and drop it to the row of the sub-calendar and the date you want the copied event to be on. Adjust the date range to include both dates of the original event and the copied event.

Option 3: Use the Duplicate function
Right-click an event, select Duplicate. The event editor will pop up with the original event info pre-populated except no sub-calendar is selected. You may select one or more sub-calendars and edit anything before save the new event. It’s also possible to duplicate a read-only event.