Yes, LIKEST is a Scrabble word!

Letter values in Scrabble US: L 1, I 1, K 5, E 1, S 1, T 1.

Is it a valid word?

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

resembling or similar; having the same or some of the same characteristics; often used in combination
equal in amount or value
having the same or similar characteristics
conforming in every respect