Is Zakat obligatory on the amount paid for a car not yet received, and how is it to be given, and is it obligatory on the amount not yet paid?

If the car has entered into your possession, and its delivery is delayed pending the payment of the remaining amount, then there is no zakat (definition) due on the amount you have already paid, because it has left your possession. However, if the amount paid is a deposit with the company until the full amount is completed, then zakat is due on it if it reaches the nisab (definition) by itself or in conjunction with other wealth. The method of calculating zakat is 2.5% of the amount. As for the amount that has not yet been paid, it is subject to zakat along with any other money you possess, if it is present at the time zakat becomes due. There is no zakat on nonexistent wealth.