I have found answer by myself today (took 3 months haha)
Just use timer tick This...
[C#]
textblock.Text = myMovingCanvas.RenderTransform.GetValue(CompositeTransform.TranslateXProperty).ToString();
Because storyboard's target use this properties...
[xaml]
<DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.RenderTransform).(CompositeTransform.TranslateX)" Storyboard.TargetName="myMovingCanvas"