We did something similar, but ours pull items within a specific date range.  At the end of each month, the repository is searched and the expiry dates (completion date in your case) are pulled from the entries found in a particular location.

They are compared to a the time period between the current date and the date token calculator (set at six months in this example).  So if it is July 31, the date token calculator will be set up for 6 months later.  

Conditional decision branch is set to process any items that have expiry dates between the current date and the calculated date.

Then the process continues on it way.  It our case it makes a shortcut into a folder that is monitored so the manager is aware that training is necessary, but you could configure emails, too, as long as you had the original user email.