Xamarin.IOS and Xamarin.Forms.iOS Chart events now implement an EventHandler<NSSet>
    public event EventHandler<NSSet> ClickAxis;
    public event EventHandler<NSSet> ClickBackground;        
    public event EventHandler<NSSet> ClickTitle;
    public event EventHandler<NSSet> ClickLegend;  
Now these are corectly fired on both (Xamarin.Forms.iOS and Xamarin.iOS). This way (using NSSet) we get all control over the touches, i.e : 

        private void Chart_ClickLegend(object sender, NSSet e)
        {
	    // e are "touches"                 
            var touch = touches.AnyObject as UITouch;
            var locInView = touch.LocationInView(touch.View); // Point

            Chart.Header.Text = "Legend clicked! ";
        }