Open Windchill Shell and run the command <jconsole>. You will see java gui app, that will ask you which process you want to monitoring. Select variant like "wt.method.MethodServerMain wt.method.serviceName=..." and press Connect.
Then open MBeans tab and in the folder structure open the node like:
com.ptc/Monitors/ActiveUsers/Attributes/TotalActiveUsers. In the right field in the Value string you will see: java.lang.String[usersCount]. Double click on this will open the list of users logins.