Green’s Dictionary of Slang

(US) definitely, certainly.

1893		Woolwich Gaz. 8 Sept. 3/5: ‘Whar I hit you?’ ‘In the calf of this leg.’ ‘Hit you sho’ nuff, did I?’ ‘Of course you did’.
1933		(con. 1850s) R. Bradford Kingdom Coming 84: Hit ain’t but one sho-’nuff free and dat’s in heab’m.
1934		Z.N. Hurston Jonah’s Gourd Vine (1995) 92: ‘Glad tuh see me, Lucy?’ John asked [...] ‘’Course, John.’ ‘Is you only mouf glad or yuh sho nuff glad?’.
1946		C. Himes ‘The Something in a Colored Man’ in Coll. Stories (1990) 406: Ifn you gonna bet sho nuff make it a fin.
1958		C. Himes Real Cool Killers (1969) 40: ‘A dead adolescent who’s called a Real Cool Moslem.’ ‘Sho’ ’nuff cool now,’ Haggerty slipped in sotto voce.
1963		W.C. Anderson Penelope 178: Ah’m sho’ nuff glad to heah that.
1968		N. Heard Howard Street 226: Ahm sho’ nuff glad they got that dicklicker, man.
1972		O. Hawkins Ghetto Sketches 70: I knew some cats who converted and they sho’ ’nuff righteous got they shit together.
1973		D. Goines Street Players 147: Some sure nuff good jive.
1978		R. Charles Brother Ray 53: This was the lady you’d go to if you were sick—I mean sure-enough sick.
1983		N. Heard House of Slammers 43: Lordy! [...] Chile, that sho-nuff hit the number!
1992		J. Mowry Way Past Cool 40: Maaaan, you sho nuff got some foxes in this here town!
2000		C. Cook Robbers (2001) 13: That brake fluid done stained my pants. The Ranger took a look. I’ll be, it sure nuff did.
2005		L. Theroux Call of the Weird (2006) 192: I’m out there tryin’ to chase that cheddar, ’cause cheddar sho ’noff make it better.