Killer Kane has already made contact with Iggy when he and Max arrive at the Testaments "seeking shelter." Kane has apparently warned Iggy about there being no alcohol around since he is trying out his new character, the Reverend Kenneth David Kane; but Loretta has been drinking "a little punch," and Iggy assures Kane that "She's okay." Iggy reports that he has found a suitable apartment for Kenny and Max to use as a hide out: The old woman who lives there is out-of-town visiting her sister, and the apartment is along a back alley that is not visible from the main road. Iggy later reports that the cops had paid him a visit: They were looking for Max and his father, and they had Kevin in the police car with them. Kenny later demands that Iggy bring him a "firearm... Something small but functional..."--and to secure "transportation" for them to escape.

What does Iggy report to Killer Kane in the apartment?

Actually, it would be more appropriate to say that Kenny “Killer” Kane is the one who comes to the apartment.  However, you are right that Iggy “reports” something important to Kane. The apartment in question is Iggy’s and Loretta’s apartment in the New Testaments (the tenements in town). Kane has already kidnapped his son, Max, on Christmas Eve. As Kane arrives with Max bound and in tow, Loretta is drunk (not surprisingly). Kane immediately gets angry at Iggy about Loretta’s drunken stupor because it may interfere with his plan. Iggy is afraid of Kane, which is obvious due to his stammering and his speech. Kane then orders Iggy to procure some food for “me and my boy.” Iggy then fries burgers while Loretta passes out. It is at this point that Iggy “reports” what you mention in your question. What Iggy says is, “Any time you want, I’ll show you that place I told you about.” Iggy is talking about finding a spot to hold Max that is both secret and private. Iggy has found an old basement in an elderly woman’s home that would be perfect for keeping Max imprisoned. This is what Iggy reports to Kane. As soon as Iggy reports this, Kane insists on seeing the place.