We are looking to track the actual usage of personal certs in our organization. I am not able to find where I can see that information. Any guidance would be greatly appreciated.
Not sure there's anything you can use here. There's the "Message encryption report", but it covers messages protected by OME and sensitivity labels afaik, not S/MIME. You can look into using (extended) message trace to fetch some info, that's probably your best bet.