A piercer.
A psychologist is the proper name for someone who studies the mind.
The proper name for someone who speaks four languages is a quadrilingual.
combustion
If you mean the species of tree, it is not a proper noun. However, if you were to name someone or something "Birch" - it is a proper noun.
Chandler
It is a proper noun because it is the name if someone
The name of someone who gives and completes a hearing test is an audiologist.
It is a proper noun, as it is the name of someone.
Because someone didn't know the proper terminology and made up a name. Technically, it is simply a philtrum and a labret. Most of these "___ bites" names seem to simply be made up either by people who want a name to describe a specific pairing of piercings or by people who just want to look cool and don't think "paired labrets on the right side" works as well. (Yes, all lower lip piercings are technically "labrets" and all upper lip piercings are technically "philtrums.")
Yes, the name Penny is a proper noun because it is a specific name used to refer to a particular person or thing. It is capitalized when used as a name for someone.
No, not unless that's someone or something's name.
As a proper noun as someone's name, yes.