There is no specific profession or label to the study of vehicles. A car enthusiast maybe called a petrolhead while an auto mechanic is the profession of a person that specializes in diagnosing and fixing vehicles.
An automotive enthusiast.
What is the name of a person that studies organisms
A person who studies bees is called an apiologist.
An entomologist is a person who studies insects.
A person who studies audiology would be called an audiologist.
What is the name of a person that studies derivation of
mr. djw studies dinos