A doniker (or donniker) refers to a toilet or bathroom in circus and carnival slang. A doniker location (or “doniker loke”) refers to a crummy location for a game or setup.
According to goodmagic.com, the term doniker was
Derived from ‘dunnekin,’ in common use among lower-class Britons in the 1700s meaning ‘outhouse.’ Probably derived from ‘dung’ and “-kin”, a suffix referring to a small container or private room (many euphemisms for ‘bathroom’ refer to it as a ‘closet’ or ‘the small room’). In Australian slang today, an outhouse is a “dunny.”
Another possible explanation for the origin of this word is the need to pull down one’s knickers.