In Attaché, there is no specific command that a Supervisor user or user with Supervisor rights can run to log out another user.
However, you can restart the Attaché services, which effectively does the same thing in logging users out of Attaché. It will however, log ALL users out. So, you would use this feature only after letting other logged in users know you are going to do so, especially if they are in the middle of performing transactions. If you log them out without advising, they may lose transactions or end up with partially updated transactions.
You can confirm who is logged into Attaché before restarting the services to advise those users you are restarting the services.