You could subscribe to these notifications yourself within the ViewController that manages the SKView. Then you don't have to navigate some weird hierarchy to obtain it.
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(willEnterBackground)
name:UIApplicationDidEnterBackgroundNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(willEnterForeground)
name:UIApplicationWillEnterForegroundNotification
object:nil];
- (void)willEnterForeground {
self.skView.paused = NO;
}
- (void)willEnterBackground {
// pause it and remember to resume the animation when we enter the foreground
self.skView.paused = YES;
}