Yes, ASSIGNEE is a Scrabble word!

Letter values in Scrabble US: A 1, S 1, S 1, I 1, G 2, N 1, E 1, E 1.

Is it a valid word?

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

(law) the party to whom something is assigned (e.g., someone to whom a right or property is legally transferred)