What is the value of a 1992 P copper nickel?

There is no such coin. All US nickels except the famous "war nickels" of 1942-45 have been made of an alloy of 75% copper and 25% nickel.

If your coin appears to be copper, it could be plated or it could be discolored from exposure to chemicals or heat.

If you're absolutely certain it's not made of cupronickel it should be evaluated by an experienced dealer or appraiser who can check its composition, but it's extremely unlikely to be anything other than an ordinary 5¢ coin.