Currently connected VNC Viewer users can be monitored from RealVNC Server's Information Center, which is accessed using the RealVNC Server taskbar icon:

Viewing details of connected VNC Viewers

You can view details for each connected user, such as where they are connecting from and the permissions level they have for their connection, as well as disconnect them:

Disconnecting VNC Viewers

As well as being able to disconnect individual VNC Viewers as shown above, RealVNC Server provides an option to disconnect all connected VNC Viewers simultaneously:

Connection notifications

By default, the RealVNC Server user is notified when VNC Viewer users connect and disconnect:

If you would like to turn the notifications off, you can do so using RealVNC Server's Options dialog, using the Notify when users connect and disconnect checkbox in the Privacy section:

Alternatively, you can configure RealVNC Server to always display the name of the connected user, or, if multiple VNC Viewer users are connected, the name of the most recently connected user, by changing the ConnNotifyAlways parameter to True in RealVNC Server's Options dialog, Expert section.