Green’s Dictionary of Slang

a general intensifier for a question.

1916		Tomahawk (White Earth, Becker Co., MN) 19 Oct. 3/5: Who in all-fired hell are you talkin’ about?
1935		J. Masefield Victorious Troy 68: ‘Who in hell said “Time, too?”’ Cobb asked [...] ‘Which of your damned packet-rats said “Time, too”?’ .
1959		C. Himes Crazy Kill 29: Who in the God-damned hell’s going to bring him in?
1963		B. Hecht Gaily, Gaily 96: Who in hell knows her name?
1982		R.M. Brown Southern Discomfort (1983) 78: A pounding at the back door scared her. ‘Goddamit!’ [...] ‘Who in fucking red hell is it?’.