How to logout or kill other user session?
Well, let’s start saying that you need to be root to do that, and that it is not polite or a good idea to do that, unless that user is not logged with permission.
It is always better to politely ask her to logout by herself, using the wall, command. But, let’s suppose you really want to logout that user. Use the command
skill -KILL -u [user]
Replace [user] with the username of the user you want to kill, if you only want to stop for a while his / her session, enter at prompt as root:
skill -STOP -u [user]
Once you decide to let [user] continue using the system run:
skill -CONT -u [user]
Once again replase [user] with the username of the user you want to interact with.
Read skill man page, for more options.