Is there a way to see what specific device is being used to watch specific shows on my Trakt account? There are many on there that we have not watched.
You aren't able to see which app or add-on added activity to your account, but you can see all authorized ones here: https://trakt.tv/oauth/authorized_applications. You can revoke authorization for all and add them back as you use them to help track down which is causing the issues. Revoking and reauthorizing also fixes a lot of sync issues, so you could revoke at https://trakt.tv/oauth/authorized_applications, and then re-authorize each app or add-on immediately and see if you're still getting unknown activity added to your history.