Should a Dr. Seuss book be referenced by this name or his real name, theodor Geisel?

Personally i would reference to his writing name (Dr. Suess) and not his real name, this is quite common and also allows others who don't know the authors real name to understand you. Most people call Joanne Murray, J.K Rowling, because if you asked a Harry Potter fan who Joanne Murray was, they wouldn't understand you, so just stick with Dr. Suess.