Deanna R. answered 04/11/19
Professional Digital and Traditional Artist
Theoretically, you don't have to know much of anything to be a good designer. I mean, theoretically you can draw well without knowing any of the "art rules," either.
However, most of us aren't gifted with some divine talent that makes us able to think of exactly what we want and create it without any practice whatsoever. The reason we learn how to draw to become a graphic designer is that you learn several secondary skills while learning to draw. You learn the importance of values and color theory. You learn what goes well with what you have to work with and you're more likely to find creative and innovative ways to do whatever task is at hand. You also learn how to visualize other peoples' visions, which is something every artist-for-hire needs to learn.
I would say you don't *techincally* need any knowledge of fine art to be a successful graphic designer, but I would also be more likely to hire a graphic designer that does.