My business is quoting this job and his insurance requires us to have works compensation, we legally don't need it otherwise in the state of New Hampshire because we're both owners so we can be exempt from the policy our business does cover works comp we r just exempt to save some money. I'm wondering can we get a single job policy just for this job?
Maybe. Sort of.
In some states, you can get a "minimum premium" policy "for certificate purposes". However, if you cancel it after that job, you don't get any money back.
The BIG question is, how much would it cost you, and can you GET this type of policy in NH (I've written them in MA, but not NH). So you'd need to talk to the agent that does the rest of your business insurance, to see if it's possible, and how much it would cost you. Depending on the type of business, it's not unreasonable to expect it to cost you $1,000 to $2,000, or even more. You'd factor that into your quote.
You probably need to do this sooner or later, because just about ANY business you do work for, is going to require it.