The answer is the 2nd sentence, "John though his sophistication would win the love of Ellen."
Here's why:
abstract noun: a noun denoting an idea, quality, or state rather than a concrete object.
Sentence 1: the noun is "box", a concrete object.
Sentence 2: the noun is "sophistication", which is a quality, not a concrete object.
Sentence 3: the noun is "car", which is a concrete object.
Sentence 4: the noun is "mirror", a concrete object.