I bought a project boat this winter, I have the title for the boat but the trailer has no title or registration .So how do I go about getting it registered?

grind off the vin number put a new coat of paint on it and tell them its a homemade trailer you need to title.

Might just give a call to who ever does the titling and ask them. Many states don't require a trailer title or license for boat trailers (KY doesn't)

You can do what Ben says or find the original number and have someone do a title search as long as you are sure it doesn't have a shady past.

grind off the vin number put a new coat of paint on it and tell them its a homemade trailer you need to title. Yes do this then google one of the Maine registration sites and get it titled and tagged in Maine. Very easy to do and cheap. They will walk you thru it. All legal and be done in couple of day for very cheap.

https://mainetrailer.com/trailer-registrations or the Staab Registration site

I actually had a girl at the DMV in California tell me to go home, build a new trailer with all the frailer parts I had except for the part with the numbers and bring it back the next day. ( an old roommate gave me the trailer, it hadn't been registered in years and they wanted more in back registration than the trailer cost new) So I did, they gave me new numbers and life was good.

Oklahoma the boat registration is the trailer registration too. Bizarre .
Some states there are gvwr steps where say under 5000 lbs ,can do homebuilt , but over , must be inspected and titled

Maryland you have to take it to state police for inspection. I'm sure Jersey is no better???
Can you do Maine Reg out of state?

Yes. I've done it several times. 5year tags for $99 vs paying out the ass every 2 years in MD