To access your log
Go to the Subscriptions or Perpetual Purchases section, depending on which type of license you own.
Locate the account for the Activation Log you wish to view and click "Edit Activations".
Click on the blue "View Activation log" button.
This will open a pop-up with a history of all users who have/had a license.
Note that "Activated" users (green box) are currently assigned a license, while "Deactivated" (red box) users have been unassigned.
As this is a history, you will still see when a user was assigned, even after they've been removed as a user. The most recent action will be at the top of the list.