If my car got stolen from a car shop, who is responsible for damage done to it?

The car shop is liable for negligence.  Negligence is the failure to exercise due care (that degree of care that a reasonable car shop would have exercised under the same or similar circumstances to prevent foreseeable harm).  Your damages (the amount of compensation you are seeking in your lawsuit) would be the cost of repairs to your car.  If you need a rental car while your car is being repaired, that cost should also be included in your damages.  You will need to mitigate (minimize) damages by selecting a rental car with a reasonable rate.  If you were to select the most expensive rental car you could find, you have failed to mitigate damages and your damages would be reduced accordingly.

The person who stole your car could also be named as a defendant in your lawsuit.  The thief would be liable for conversion (this is a type of theft in a civil case).  Your damages for conversion would be the value of your car.  You would file one lawsuit naming both the auto shop and the thief as defendants.  Your lawsuit would have separate causes of action (claims) for negligence and conversion.  There would also be a separate criminal case against the thief for auto theft.