Get your OEM Windows 10 Installation Key

Where is the Windows 10 installation key stored on your machine?

You can find the key in your Windows Registry Editor

Click on Windows icon and type “registry” in the navigation bar paste the fallowing path:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform

Or search for phrase BackupProductKeyDefault in keys name.

Get Windows 10 installation key from terminal

You might try to get the code from terminal, but in my case this not always work. If you want to give it a try open CMD as administrator and run the fallowing command:

wmic path SoftwareLicensingService get OA3xOriginalProductKey

The above return for me an empty line. But the below command worked for me. From CMD terminal run:

for /F "tokens=3" %A in ('reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform" /v "BackupProductKeyDefault"') DO (Echo %A)

https://www.howtogeek.com/206329/how-to-find-your-lost-windows-or-office-product-keys/
https://stackoverflow.com/questions/53961305/how-to-get-data-from-a-registry-key-value-via-command-line