If your vehicle was sold for more than $500, you should have received a Form 1098-C, Contributions of Motor Vehicles, Boats, and Airplanes" from the organization you donated your car to.
If you did not receive a Form 1098-C, contact the organization you donated your car to. They will have all of the information on that donation form.
If you did not receive this form, it means that your donation was valued at less than $500.