After you %hook a class, inside the method you're using, do the following if for example you're trying to get the icon for the mail app
// Get the SBApplication for the mail app
Class $SBApplicationController = objc_getClass("SBApplicationController");
SBApplication *mailApp = [[$SBApplicationController sharedInstance] applicationWithDisplayIdentifier:@"com.apple.mobilemail"];
// Get the SBApplicationIcon for the mail app
SBApplicationIcon *mailAppIcon = [[objc_getClass("SBApplicationIcon") alloc] initWithApplication:mailApp];
The important thing is to get the right DisplayIdentifier of the app you're interested in.
Hope this help! any problems please shout.