There isn't a single, universally known set of aphorisms adorning the walls of a *specific* study room library at Harvard University. Harvard has many libraries, and countless rooms within them. Each might have its own decorative elements, some possibly including aphorisms, but there's no famous, widely publicized collection like, say, the Ten Commandments on a courthouse wall.
If you're thinking of a specific library or room (perhaps you saw it in a picture or film), providing more details would help. Otherwise, the idea of a set of aphorisms on the walls of a Harvard study room is a general possibility, not a specific, documented fact.