Answer:
A student sometimes discovers he or she doesn't like their chosen field.
Explanation:
The pronoun-antecedent agreement simply means that the pronoun agrees with the antecedent in number which can either be singular or plural (pronoun) or first person, second person, etc (antecedent).
The sentence that has a problem with the pronoun-antecedent agreement is A student sometimes discovers he or she doesn't like their chosen field because the pronoun does not agree with the antecedent in number.
