MobaXterm has a built in X server. The default configuration in MobaXterm is to run X server.
To make sure:
1.Press the “Settings” button to open “MobaXterm Configuration” window. Select X11 tab and see that option “Automatically start X server at MobaXterm start up” is selected.
2. Right click on the session you configured for the cluster and select “Edit session”. Under “Advanced SSH settings” see that “X11-Forwarding” is selected.