Use Nirsoft’s ProduKey:
Run the program as Admin (it will show your own key by default)
Press F9 to bring up the Select Source dialog
Select Load the product keys from external Software Registry hive
Browse to the SOFTWARE registry hive. For example, if you have the drive from the other system mounted as drive Z:, then you would probably select Z:\Windows\System32\Config\SOFTWARE
Click [OK]
Save info as TXT file
