phrenologist
A person who practices phrenology, the study of skull shapes to determine character and mental faculties. This is a historical term; phrenology is now discredited.
In the 19th century, phrenologists tried to judge character from the shape of the skull.
骨相学 is the study of phrenology itself, while 骨相学者 refers to a person who practices it.
Compound of 骨相 (こっそう, 'skull shape; phrenology') + 学者 (がくしゃ, 'scholar'). The exact historical derivation is uncertain, but the term follows a standard pattern for naming specialists in a field.