x11vnc – a real X11 display.

Sometimes one wants to connect to a real X11 display (i.e. one attached to a physical monitor, keyboard, and mouse: a Workstation or a SunRay session) from far away. Maybe you want to close down an application cleanly rather than using kill, or want to work a bit in an already running application, or would like to help a distant colleague solve a problem with their desktop, or would just like to work out on the deck for a while. This is where x11vnc is useful.
and here you can find a lot more information: http://www.karlrunge.com/x11vnc/

install x11vnc and then on remote machine as user type:

x11vnc -display :0

and then on your local machine type:

vncviewer IP