Something like: root.getRect(stage).intersects(clip.getRect(stage)) && clip.visible && clip.alpha
I'm not sure about mask / clipRect / ColorMatrixFilter (they all may make the clip appear as invisible) + of course, there may be another display object on top of the clip, which you can roughly check by getObjectsUnderPoint() providing all 4 points of the rectangle generated from intersection of the clip and root rectangles, but this may not work most of the time, if clips aren't rectangles by themselves / are rotated etc...
