Sometimes you might need your key for Windows, like when you want to to a bare metal rebuild. There isn’t (that I could find) a way to get it from the GUI, but there is a command you can run from the command prompt (don’t forget to run the command prompt as Administrator) that will give you your key:
wmic path SoftwareLicensingService get OA3xOriginalProductKeyIt’s completely intuitive, like most Windows command line commands.