Yes, CONKED is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, K 5, E 1, D 2.

Is it a valid word?

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

come to a stop
hit, especially on the head
pass from physical life and lose all bodily attributes and functions necessary to sustain life
pass out from weakness, physical or emotional distress due to a loss of blood supply to the brain

Also: pass away, kick the bucket, cash in one's chips, buy the farm, give-up the ghost, drop dead, pop off, snuff it, pass out.