Getting Position.Y of parent node with physicsBodies - sprite-kit

Question

Im trying to see when my circleGroup Class Object has left the screen
(am pretty new at this so any suggestions welcome!)
including any other way to remove the class once it is off screen
circleGroup Class contains a blank SKSpriteNode, and 8 other sprites are grouped around the blank SKSpriteNode as children (these have physics),
Gamelayer:
Always logs (0,0)
NSLog(#"_mycircleGroup.position.y #%f",_mycircleGroup.position.y);
//outputs myArc.position.y #0.000000
which means I can't check when Class is off screen
if (_mycircleGroup.position.y < 0)
{
NSLog(#"_mycircleGroup off screen");
//[_mycircleGroup removeFromParent];
//[self myMethod];
}
Any ideas how I might read position?
with thanks
:)
Solution,
I needed to be logging the parent node inside of the class
so in this case I have a class and in it is a parent sprite which i need to track (Since it seems like nodes with physics don't track)
if (self.myCircleClass.parentSpriteThatEveryThingIsAddedTo.position.y < 0)
{
NSLog(#"my arc off screen");
//[twoSpritesWithParticlesBridge removeFromParent];
//[self addStaticLinkedSpriteWithParticles];
}

Answer 1

As above with thanks to WangYudong for jogging my logic :P
Solution, I needed to be logging the parent node inside of the Class so in this case I have a class and in it is a parent sprite which I need to track (Since it seems like nodes with physics don't track, so I couldn't track te entire object, just the object without physics...)
if (self.myCircleClass.parentSpriteThatAllOtherSpritesParentedTo.position.y < 0)
{
NSLog(#"my arc off screen");
//[twoSpritesWithParticlesBridge removeFromParent];
//[self addStaticLinkedSpriteWithParticles];
}
Take everything with a pinch of salt, non definite and completely questionable! (since I'm new at coding), but hope it helps someone :)