Try creating a flow designer:
1.- Go to Process Automation -> Flow Designer.
2.- New Flow and fill the information.
3.- I recommend to Repeat every day, you can change this parte in accord with your necessities.
4.- In actions create 1 Action "Look Up Records"
5.- Selec kb_knowledge as a table
6.- Add your condition for expiring date article
7- Select a Flow Logic For Each Item in the look up
8.- Select a Send Email Action
9.- Select the Target Record for your for Each
10. In you To, select the created by or your owner field, from your For each logic.
11.- Add the subject and body of your email.
12.- Save, activate and test
Maybe the email look like this:
Hope that help you
