Green’s Dictionary of Slang

cook v.2

[Yid. geb a kook, to spy out, to see]

(Aus. Und.) to see, to to notice.

[Aus]Sydney Sportsman (Surry Hills, NSW) 8 Jan. 1/5: It is understood that the enterprising gentleman’s ‘clerk’ had ducked his nut the moment he cooked the copper coming, and done a guy at a shade outside 2½ yards worse than evens.

In derivatives

kooker (n.)

(Aus.) one who conducts a surveillance.

[Aus]Truth (Sydney) 9 Feb. 4/6: Plane close kookers, with the wardens, / Works their emag, hand in hand.