Find Windows Product Key

Press Windows key + X.

Click Command Prompt (Admin)At the command prompt, 

type: wmic path SoftwareLicensingService get OA3xOriginalProductKey

This will reveal the product key. Volume License Product Key Activation.

 

update:
powershell "(Get-WmiObject -query 'select * from SoftwareLicensingService').OA3xOriginalProductKey"