We can see images in UV window.
But, instead of a image, how to see a texture in UV window, like marble procedural texture?
select what you want to unwrap in the edit mode press u unwrap then go to the picture uv layout panel dont change the mode just go to the uv map editor and open or load the image you want haha.
I believe the only way to ‘see’ a procedural in the image editor mapped to uv is to uv unwrap your mesh, map it to a new blank image, and use the Bake Tab in the render buttons to bake the texture to the image, and then save the image. If you just want to be able to preview the procedural and make adjustments, you can go to object mode and use Shift-P to open the preview window over your mesh.