An automotive technician.
you call them a computer tech
mechanic car-bore-ator
You can call a person who knows what they want assertive, decisive, or self-assured.
vulcanologist.
call a couple of junk yards, and compare answers...you'll probably find a person that knows for certain... good luck d
A Skeptic person
A person who knows three languages is typically referred to as a trilingual.
Educated.
a lair
annoying
Smart.