Yes, QUIDDITY is a Scrabble word!

Letter values in Scrabble US: Q 10, U 1, I 1, D 2, D 2, I 1, T 1, Y 4.

Is it a valid word?

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

an evasion of the point of an argument by raising irrelevant distinctions or objections
the essence that makes something the kind of thing it is and makes it different from any other