I got mine many years ago. Even if you are an experience rider, you need to take a written test (everyone needs to take the written test). Motor Vehicle Commission (MVC) used to have a booklet to prepare you for the motorcycle test. After you get you motorcycle learners permit, you can ride with a licensed motorcyclist until you take the road test -- at least back then they had a road test. It was basic stuff, starting, stopping. rubber cone slow speed slalom, rubber cone slow speed figure eight (no touching the ground on the slalom and figure eight).
I understand that now if you go through a motorcycle safety foundation course, you are issued your motorcycle endorsement when you present your certificate of completion to MVC. Not sure how that works if you took a MSF course elsewhere, or how recent it must be.
Here is a link to the MVC site regarding what you need to do to obtain a motorcyle endorsement on a NJ driver's license:
http://www.state.nj.us/mvc/Licenses/mot ... endors.htmk_enn