public Geometry GetDrawingOutline( 
   long oid,
   MapView view,
   DrawingOutlineType outlineType
)

var featureLayer = MapView.Active.Map.GetLayersAsFlattenedList()
                           .OfType<BasicFeatureLayer>().FirstOrDefault();
if (featureLayer == null)
  return;

var mv = MapView.Active;

QueuedTask.Run(() =>
{
  using (var table = featureLayer.GetTable())
  {
    using (var rc = table.Search())
    {
      //get the first feature...
      //...assuming at least one feature gets retrieved
      rc.MoveNext();
      var oid = rc.Current.GetObjectID();

      //Use DrawingOutlineType.BoundingEnvelope to retrieve a generalized
      //mask geometry or "Box". The mask will be in the same SpatRef as the map
      //At 2.x - var mask_geom = featureLayer.QueryDrawingOutline(oid, mv, DrawingOutlineType.Exact);
      var mask_geom = featureLayer.GetDrawingOutline(oid, mv, DrawingOutlineType.Exact);

      //TODO - use the mask geometry...
    }
  }
});

var annoLayer = MapView.Active.Map.GetLayersAsFlattenedList()
                         .OfType<AnnotationLayer>().FirstOrDefault();
if (annoLayer == null)
    return;
var mv = MapView.Active;

QueuedTask.Run(() =>
{
    //get the first annotation feature...
    //...assuming at least one feature gets selected
    using (var fc = annoLayer.GetFeatureClass())
    {
        using (var rc = fc.Search())
        {
            rc.MoveNext();
            using (var row = rc.Current)
            {
                var oid = row.GetObjectID();

                //Use DrawingOutlineType.BoundingEnvelope to retrieve a generalized
                //mask geometry or "Box". The mask will be in the same SpatRef as the map.
                //The mask will be constructed using the anno class reference scale
                //At 2.x - var mask_geom = annoLayer.QueryDrawingOutline(oid, mv, DrawingOutlineType.Exact);

                var mask_geom = annoLayer.GetDrawingOutline(oid, mv, DrawingOutlineType.Exact);
            }
        }
    }
});