Green’s Dictionary of Slang

(Aus.) a generic term for a Jew, esp. when carrying out a stereotyped job, e.g. banker or bookmaker.

1902		Bulletin (Sydney) 6 Sept. 16/3: One other, when he received a gentle hint that, unless he made jumbucks grow fat, [...] his head would fall in the basket, promptly wired to Cohen that he could go to Sheol, packed his traps in a jam-tin, and skipped for the wild and woolly West. [Ibid.] 15 Nov. 24/2: [T]he police force of Sydney exists largely to secure for the Moseses and Kohens of the big Tatt.’s clubs a close monopoly of the gambling business of the city.
1912		Bulletin (Sydney) 5 Dec. 15/2: If Cohen, or somebody, will only lend the money for the cement, the Blowhole will live again [...]. Everything – even a Blowhole – depends on Cohen nowadays.
1914		Truth (Melbourne) 14 Feb. 5/7: The little brown people with whom Bull, at the suggestion of Cohen, has entered into an unholy alliance.