Create report on use of private comments box

We were interested in creating a report that tells us whether our technicians are unchecking the private comments box or leaving it checked, so we can use this information as a training opportunity.  We trained our technicians to uncheck the box to ensure the client sees their comment, but we have heard that some people aren't remembering.  We don't specifically know who, which is why a report would help so we can approach them to provide more training.  I didn't see a report field or filter that captures the use of this box, so I'm interested in learning other ways we can accomplish this.