What is a Buffalo nickel 1919p can't find it in the red book how much is it worth?

I'm very surprised you couldn't find your coin in the Red Book. 1919 is a common date for buffalo nickels. Perhaps you're looking specifically for a "P" mint mark. Remember that Philadelphia did not use a P on nickels until WW2 and then again starting in 1980.

That means a 1919 Philadelphia nickel won't have a mint mark, nor will any other coin minted before 1980 except for those wartime nickels and 1979 dollars.

Anyway, a 1919 buffalo nickel from Philly retails for a couple of bucks in average condition, up to maybe $14 in Almost Uncirculated condition.