Software Development & Operating Systems

This works for Windows 7, 8, and 10:

The use case for this is that you have several licensed copies of the same Windows version, but do not remember which key you used on which computer.

Open the Start Menu and type:

cmd

Type the following at the command prompt:

slmgr -dli

After about 15 seconds, a dialog will popup displaying a partial product key.  In my case it was the last segment of the key.