public virtual object GetOriginalValue( 
   int index
)

// Set up a listener for row change events on the table associated with the
// provided feature layer. The event subscription occurs within a queued task to ensure thread safety.
await QueuedTask.Run(() =>
 {
   //Listen to the RowChangedEvent that occurs when a Row is changed.
   var modifiedFeatureLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>().FirstOrDefault(); ;
   RowChangedEvent.Subscribe(rowChangedEventArgs =>
     {
       // RowEvent callbacks are always called on the QueuedTask so there is no need 
       // to wrap your code within a QueuedTask.Run lambda.

       //Get the layer's definition
       var lyrDefn = modifiedFeatureLayer.GetFeatureClass().GetDefinition();
       //Get the shape field of the feature class
       string shapeField = lyrDefn.GetShapeField();
       //Index of the shape field
       var shapeIndex = lyrDefn.FindField(shapeField);
       //Original geometry of the modified row
       var geomOrig = rowChangedEventArgs.Row.GetOriginalValue(shapeIndex) as Geometry;
       //New geometry of the modified row
       var geomNew = rowChangedEventArgs.Row[shapeIndex] as Geometry;
       //Compare the two
       bool shapeChanged = geomOrig.IsEqual(geomNew);
       if (shapeChanged)
       {
         // The geometry has not changed
         Console.WriteLine("Geometry has not changed");
       }
       else
       {
         // The geometry has changed
         Console.WriteLine("Geometry has changed");
       }
     }, modifiedFeatureLayer.GetTable());
 });