how do i get the owner of a car based on nj license plate

There are many, many places on the internet that offer license plate
record search services. Of course, most if not all of them are not
free. The fees vary from website to website. Two examples are:

http://www.licenseplate.net/states/new_jersey/
http://www.efindoutthetruth.com/LicensePlateSearches.htm

Found these websites by using Google with the following keywords:

"license plate" "new jersey" record

Good luck!