The correct answer is "no one would ever use"
Explanation:
In language, an adjective clause refers to a set of words that contain a subject and a noun and describe or define another noun. These clauses should not be confused with the main elements in a sentence, because they only complement or provide more information about a noun by describing it. This implies, in the sentence "The trunk was full of junk no one would ever use" the adjective clause is "no one would ever use" because this set of words describe the noun "junk", also they contain a noun (no one) and a verb (would use).
