property targetId

This property sets and gets the identifier of a valid target instance. This is the DOM id of a valid UI element (box), or a built-in keyword to denote a relative box (_self, _parent, _nextSibling, _root, etc.)

function onSample()
{
    var box = scene.getBoxById("myBox");
    if (box)
    {
        var binding = box.getDataBinding("myBinding");
        if (binding)
        {
            var targetId = binding.targetId;
            if (targetId)
            {
                shell.print("Target id = " + targetId);
            }
        }
    }
}