Open admin Command prompt:
then type slmgr -dlv <enter>
Under the Partial Product Key, you will see the last 5 characters (-XXXXX) of the key in use.
If these are unknown to you, You can post these characters here, or you could google "-XXXXX" which should tell you if this is a generic Windows 10 key.
The only other Microsoft program that is generally available that I know which will tell you your FULL key is the Media Creation Tool*, once it has been run, in the file:
C:\$Windows.~BT\Sources\Panther\ windlp.state.xml (which needs to be copied out of the folder to another location like desktop or documents, and it then should open in Internet Explorer, or another browser.)
In the following group of lines about 2/3rds of the way down the file you should find Product Key:
*Windows 10 ISO Download - Windows 10 Forums for instructions.
<ImageName>Windows 10 Pro Insider Preview</ImageName>
The Media Creation Tool would need to be run from each system that you wish to know the full product key details.