Green’s Dictionary of Slang

(US black) to look; to see.

1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 255: focus (v.): to look, to see.
1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1947		M.H. Boulware Jive and Sl. n.p.: Focus ... Eye-sight.