I am pretty new to iOS, objective C and working with Xcode. I only did one simple news type app, but now I would like to create a game I had published on another platform.>
I never used the SKSprite framework but I will try to help. First, your function "-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event" has to be set in your custom SKSpriteNode class, if not it's normal if that doesn't work.
If it's already done, you have to search where the tap is handle (by an other object) then you can use : "- (BOOL)gestureRecognizer:(UIPanGestureRecognizer )gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UISwipeGestureRecognizer)otherGestureRecognizer"
hope that will help !