I am using Lacerte, but I would assume the path would be similar.  Just substitute the like folder with the Proseries equivalent.

I have Lacerte in the cloud, so you have to find the Lacerte or Proseries folder on your hard drive and then:

Folder: 19tax

Folder: OPTION19

File: "Firms"   Open this file in Notepad and find the number that is between these "<" and ">" (the tech I talked to called them alligator jaws...you and I call them "less than" and "greater than".  The number between the alligator jaws is your Realm ID.  Hope this helps!

Dave