Hi there,

If you highlight the client's extension in the EF Center, then press F12 on your keyboard (or go to the E-File menu at the top of ProSeries > Electronic Filing > Electronic Filing Reports), you can choose from a few different reports that may have the info you need. 

I don't have any accepted extensions to check on, but the Electronic Filing Client Details report prints the extension submission ID so I suspect others would include that info, too. Just make sure to select the option to create report for "Selected Electronic Filing Records" in this window so multiple clients' details aren't included.