My ex husband quit paying child support on our 20 year old daughter because she switched from a university to a trade school that will earn her a degree in a year, does he have the right to do this, he says that she's not a college student now

What is the child custody / support agreement state. It is totally up to that. Most use wording such as "secondary" school. Then you will have to go to case law of your state to see how that has been defined by the courts.

Many chid suuport agreements don't require any payment past 18,
So time to get yours out and see what it says