I'm not sure exactly which 'Dark Knight Cover Graphic Novel' you're referring to, but often for the Dark Knight series, artists like Jim Lee might be involved. He has a very distinct style that would be great for creating a cover that stands out.
Well, different editions of the 'Dark Knight Cover Graphic Novel' may have different artists. However, in the world of Batman and the Dark Knight, some of the big names could be involved. Greg Capullo has worked on Batman comics and might be a candidate for contributing to the cover art. His dark and detailed style would fit well with the Dark Knight aesthetic. Also, David Finch is another artist whose work on Batman - related projects makes him a possible contributor to the cover of this graphic novel. Their skills in depicting the brooding nature of Batman and the overall dark atmosphere of Gotham would be crucial in creating an impactful cover.