This help page is for version 8.3. The latest available help is for version 9.3.
Remote Desktop (RD) Gateway Monitor
The RD Gateway monitor is used to periodically retrieve a list of Remote Desktop sessions connected to the Gateway
There is no configuration for the monitor and it doesn't presently fire alerts. It is just used for reporting. The chart above would be shown on a Server Status Report.
The RD Gateway Monitor can report on Remote Desktop sessions on a per-user, per-connected resource or per-gateway basis.