My ex-wife is trying to get me to pay for my 24 year olds student loan. Can a judge in New Jersey force me to do so,

Only if this is stipulated to in a divorce settlement agreement you signed years ago that you would contribute to the kid's college education OR you are a cosigner on a student loan for the kid. Otherwise your ex is not going to prevail.

Did you EVER verbally say to her that you would pay half of the kid's education or is she just saying you did? What proof does she have other than her big mouth to show the Judge that you agreed to pay for anything? The kid is 24 and is now a full grown adult who should happily pay for his own college.

Has she filed paperwork with the Courts or is she just threatening to do this?