Yes, MANIOC is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, N 1, I 1, O 1, C 3.

Is it a valid word?

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

a starch made by leaching and drying the root of the cassava plant; the source of tapioca; a staple food in the tropics
cassava root eaten as a staple food after drying and leaching; source of tapioca
cassava with long tuberous edible roots and soft brittle stems; used especially to make cassiri (an intoxicating drink) and tapioca

Also: cassava starch, bitter cassava, tapioca plant, manihot esculenta, manihot utilissima.

Not playable in Scrabble US: MANDIOC, GARI.