Yes, KNIVES is a Scrabble word!

Letter values in Scrabble US: K 5, N 1, I 1, V 4, E 1, S 1.

Is it a valid word?

KNIVES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

edge tool used as a cutting instrument; has a pointed blade with a sharp edge and a handle
a weapon with a handle and blade with a sharp point
any long thin projection that is transient