Is disc jockey a common noun?

They are born common nouns. Common nouns are words for any person, place, thing, or idea: person - man, teacher, mother, grocer, ballerina, neighbor place - country, capital, city, ocean, wildlife...

The word "you" is a second person pronoun. It is not a noun.

a common noun is a word that should not be capatilized like winter and she and my but you do capitilize it only when it is starting a new sentence while a proper noun should be like Mary and Tom or...

The word 'me' is a pronoun, not a noun.

"Apple" is a noun. Generally it is a common noun, e.g the apple tasted good. It can, however, also be a proper noun when used as a name, e.g, Apple Inc.