Green’s Dictionary of Slang

clueless adj.

stupid, ignorant, incompetent.

1943		C.H. Ward-Jackson It’s a Piece of Cake 22: ‘I’m clueless’ I don’t know; or, ‘He’s a clueless type’ the opposite of a gen wallah.
1958		E. Dundy Dud Avocado (1960) 182: He really looks such a boring little man, doesn’t he, so utterly clueless in those revolting American clothes.
1959		A. Sinclair My Friend Judas (1963) 130: He really was a clueless kind of pill.
1976		D. Ireland Glass Canoe (1982) 220: Then the clueless young kid walked in.
1977		(con. 1941) R. Beilby Gunner 119: Clueless, he thought, turning back to Whiteside: just bloody clueless and army-happy!
1982		Eble Campus Sl. Fall 1: clueless – unaware of what’s going on.
1983		(con. 1940s) D. Nobbs Second From Last in the Sack Race 176: Oh, I’m all in favour of clueless clots.
1989		M. Dibdin Tryst 36: Unlike the clueless wankers he lived with, Jimmy had always known that there was more to life than glue and cider.
1994		Eble Campus Sl. Apr. 2: clueless – lacking awareness.
1998		I. Welsh Filth 198: This whole fuckin place [is] stuffed full of the most clueless cunts that ever hid behind a polisman’s uniform.
2001		N. Griffiths Sheepshagger 129: No, you clueless cow.

In derivatives

cluelessness (n.)

ignorance, stupidity.

1989		M. Amis London Fields 107: [He] found himself in a rare state of total cluelessness.
2019		V.D. Hanson Case for Trump 147: [W]hat ensured Trump’s unlikely rise was not just Democratic cluelessness in the general election.