I’m not sure if you can get the actual desktop display in Godot, at least not with anything built-in.
For displaying the screen, you can use a TextureRect node with the texture set to the display. You may want to set the expand
property true and then the layout set to take the full rect, if you want it to take up the entire screen.
If you want to display the image in 3D, then you’ll want to use a MeshInstance node with the albedo texture set to the texture of the display. The GUI in 3D demo on the Godot demo repository may help as a reference.