Like the title!
First you need to enable cheats
EnableCheats true
Then you can dump the session information to the log
DumpOnlineSessionState
Note that it will not be dumped to the console so you have to either view the output log while debugging or run the game with the command-line argument -log to have a log window.
If Playing-In-Editor you can look in the “output log” window.
In the log look for “RegisteredPlayers”. This is the list of the current players including the listen-server itself.