There's only one way that SHOULD be possible - if someone else has access to the Google account signed in to the device. Log in to that account on myaccount.google.com from a browser then go to Device Activity & Security Events and you should see the devices that have signed in to the account.
If you need additional help or have more questions or details to share, please join the site so you can reply in this thread. See this link for instructions on how to join Android Central.