Green’s Dictionary of Slang

a general intensifier for a question; var. on what the hell...? phr.

1837		‘Nights At Sea’ Bentley’s Misc. June 624: Why, where the h-- is he to coil away his outrigger in a pair of tight leather rudder casings over his starn?
1865		Leaves from Diary of Celebrated Burglar 13/2: ‘Where to?’ says cabby. ‘Where the h—l you like, only drive on,’ we replied.
1927		(con. 1900s) S. Lewis Elmer Gantry 20: Where the hell would I get any money from before the first?
1944		‘F. Bonnamy’ A Rope of Sand (1947) 129: You ask Mason politely where the sizzling hell his boat was.
1958		F. Norman Bang To Rights 70: Where the hell did you get this from.
1960		C. Cooper Jr Scene (1996) 27: Garver! [...] Where the hell have you been?
1989		Viz June–July 42: Roger! Where the hell are you?
2000		Guardian G2 3 Feb. 7: Working out where the hell we were going to take a leak.