Yes, BENCHMARK is a Scrabble word!

Letter values in Scrabble US: B 3, E 1, N 1, C 3, H 4, M 3, A 1, R 1, K 5.

Is it a valid word?

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

a standard by which something can be measured or judged
a surveyor's mark on a permanent object of predetermined position and elevation used as a reference point

Also: bench mark.