How to access objects of SKSpriteNode subclass when moving them (Swift)

I am confused with the objects of my class Card that is the subclass of SKSpriteNode. How do I get access to these objects when a user move them. So far I can only access SKNode objects overriding touchesEnded function.

override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
    let touch : UITouch = touches.first as UITouch!
    let touchLocation = touch.locationInNode(self)
    touchedNode = self.nodeAtPoint(touchLocation)
    touchedNode.position = CGPoint(x: size.width * 0.5, y: size.height * 0.5)
    touchedNode.zPosition = 0
}

I need to know what object the user is moving but in this case when touchedNode is an object of SKNode class (not my Card object class) I am not able to figure that out.

The is operator is exactly what you need.

The is operator compares the types of the two operands. If they are of the same type, or one is a subclass of the other, the expression evaluates to true.

So you can check it like this:

if touchedNode is Card {
    // do stuff
}

Now what you might want to do is that if touchedNode is really a Card, I want to use the methods I defined in the Card class on the touchedNode.

To do this, you need to cast the touchedObject to Card:

let cardNode = touchedNode as! Card

Then you can call your methods on cardNode!