public enum DrawingOutlineType : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

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...
    }
  }
});