if i file bankruptcy while having a cosigner. who gets to keep the car? cosigner or myself?

Like many legal answers, this depends on a number of factors.  First and foremost, are the car payments being made?  If not, the lender is going to end up keeping the car!  You will be relieved from responsibility for making the car payments, whereas the lender would still be able to go after your cosigner for any unpaid balance left after the car is sold.  Assuming the car payments are being made, ownership of the car would be determined by who has the title to the vehicle.  If the vehicle is titled in your name only, your cosigner has no legal right to it.  If it's titled in both of your names then it's a matter of state contract law between the two of you who gets possession of the car--and most judges would probably award possession of the car to the party who has actually made the payments.