If you purchased your vehicle you own 100% of the vehicle. This is true even if you are still paying on the loan. If you have a co-signer for the car loan, check if they're on the title with you. Not all co-signers are co-owners. If you have a co-owner, you may only have a 50% ownership interest in the vehicle, depending on state law. Learn more about the difference between co-signers and co-owners and where to list them on your forms here.
Equity in a car is calculated as follows: (Current market value of the vehicle) - (Amount you still owe) = Total Equity. If you have a co-owner, divide the resulting equity by the number of co-owners to determine your share of the equity.
If you're leasing your car, you don't own it. Learn more about leases in bankruptcy here.