Is zakat obligatory on money invested in Murabaha to pay car installments, knowing that the total debt for the car is close to the principal and profits, and is the entire car debt or only this year's installment deducted before paying zakat?

If you have surplus wealth beyond your needs (such as real estate or cars) that can be used to pay off debt, then use it and pay zakat on the entire amount and its profits without deducting the debt. If you do not have surplus wealth, some jurists have permitted deducting the entire debt from the zakatable wealth, and you pay zakat on what remains, provided it does not fall below the nisab. The more cautious and blameless approach is not to deduct any debt at all. However, if you do deduct the debt, there is no sin upon you. It is permissible to deduct all stable debts owed by you, whether they are due immediately or deferred, for the current year or the next.