You need to consult with a lawyer for a legal, correct and current answer.
Have it examined by a gunsmith
If you're in the U.S. the short answer is, you can't.
www.airsoftatlanta.com that is where i bought all of my airsoft gun stuff at
Blue Book of Gun Values
you will need to find out if the store is still in business or contact the police if he registered it.
Long gun.
Depends on where you bought the gun. If from a store they should have the info. It might even be on your receipt. If you bought at pawn shop they usually include that info on the receipt. If you bought from individual and your state doesnt require registration you're out of luck.
If you are an adult, a legal resident of the US, and not forbidden from owning a gun because of a criminal history, and are mentally competent, yes, it is legal. There are several million legal gun owners in Texas.
It depends on the state in which you live's legislation. If your state requires registration, then I'd imagine so. You should check your state's gun laws specifically.
Go the the gunshop or person you bought it from.
If selling the gun is banned, then buying it before the ban is no problem. If owning the gun is banned then it does not matter when you bought it.