To turn on Knowledge Document Expiration Notifications, follow these steps:
1. Go to the admin tab > notifications > activity notifications, then search for "doc" - you will see an activity notification called "Document is about to expire" - click on it
2. Change the dropdown for object type to "Knowledge Documents" - it will refresh the page
3. In the notification rules tab on the bottom, click on the notification rule called "About to Expire Notification Rule"
4. Click on the Message Template that is attached to that notification rule
5. Edit that message template and check the box for "Auto Notification" then save the template
6. Close the message template, and go back to the notification rule - here, by default out of the box it will have object contacts of "Owner" and "Assignee" who will get the notification emails when a document is going to expire. You can change who is notified here in this rule, and then save it.
7. Next, go to Administration Tab > Knowledge > Documents > Document Settings, and set the number of days before expiration to send out notifications (this is 7 by default)
IMPORTANT TO NOTE: Once you save these settings and set the Auto Notify to YES on the notification template, your system will begin sending out notifications immediately for documents that will expire in X days from today (X being the number of days you set on the document settings). If there are a lot of documents that meet the criteria, then the specified object contacts will receive all of those notifications.