How do I find out who claimed me dependent on their tax return?

The IRS won't tell you that. If you believe that no one was entitled to claim you as a dependent, file a paper income tax return and take your own exemption. The IRS will sort it out. If you were a full-time student for any part of five months last year and lived with someone who was supporting you, that person is probably entitled to take you as a dependent on their tax return. If you made less than $3,400 last year and someone else provided over 1/2 of your support, you were their dependent.