Find the Windows Product Key

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

Command Prompt

wmic path softwareLicensingService get OA3xOriginalProductKey

Registry

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