According to a lie implanted in Jamie's mind by the Celestial Intervention Agency at the Second Doctor's behest, (PROSE: World Game) graphology was a subject Victoria had been dropped off to study while they went on a diplomatic mission to speak with Dastari. (TV: The Two Doctors) The nature of the subject was unclear, but the Doctor told Sardon, his CIA "handler", that it was a subject that "sounded like Victoria". (PROSE: World Game)
Behind the scenes
Unremarked in any known DWU source, graphology is the study and analysis of handwriting especially in relation to human psychology. The reason the Doctor claimed it "sounded like Victoria" is because it was one of many pseudoscientific fads primarily associated with the late Victorian era, and all but entirely discredited by the mid-20th century.