Kia ora Raechel,
I'm not aware of any way short of checking each page. Maybe a good idea to tag those pages or set up a custom field tick box so you can run a report.
I suppose if the reason for the due date set up was to create a reminder you could run a report to find those reminders and the associated courses.
But that is by no means 100%, and you have to have kept your mail logs.
Ngā mihi,
Larry