How can you find out who owns a car from the registration number?

You can attempt to get the information from the Motor Vehicle Department. HOWEVER - unless you have a valid reason for requiring the information they will probably NOT release it to you due to privacy concerns.

If you have a valid reason contact your local law enforcement agency or insurance company and they can find out for you.

Just wanting to know the address of the hot chick you saw driving the car is NOT a valid reason!