Your sense of smell suffers from sensory adaptation which means that you stop smelling something (or it becomes less strong) the more you are surrounded by it. Thus, you, your car, your apartment, or your clothes may have an odor that you have become desensitized to.
Traditional solutions such as friends, family, and your own nose you probably already use, but they all come with faults, primarily, that they too may suffer from sensory adaptation.
A device that can sense odorants in the air.
A professional smelling service. Walk in, they smell you, and give you some kind of scientific rating. No idea how to scientifically categorize smells.
While we are at it that can be another idea.