public new FeatureClassDefinition GetDefinition()

// GetDefinitionFromLayer - This code works even if the layer has a join to another table
private TableDefinition GetDefinitionFromLayer(FeatureLayer featureLayer)
{
  // Get feature class from the layer
  FeatureClass featureClass = featureLayer.GetFeatureClass();

  // Determine if feature class is a join
  if (featureClass.IsJoinedTable())
  {
    // Get join from feature class
    Join join = featureClass.GetJoin();

    // Get origin table from join
    Table originTable = join.GetOriginTable();

    // Return feature class definition from the join's origin table
    return originTable.GetDefinition();
  }
  else
  {
    return featureClass.GetDefinition();
  }
}

public RowCursor SortWorldCities(FeatureClass worldCitiesTable)
{
  using (FeatureClassDefinition featureClassDefinition = worldCitiesTable.GetDefinition())
  {
    Field countryField = featureClassDefinition.GetFields()
      .First(x => x.Name.Equals("COUNTRY_NAME"));
    Field cityNameField = featureClassDefinition.GetFields()
      .First(x => x.Name.Equals("CITY_NAME"));

    // Create SortDescription for Country field
    SortDescription countrySortDescription = new SortDescription(countryField);
    countrySortDescription.CaseSensitivity = CaseSensitivity.Insensitive;
    countrySortDescription.SortOrder = SortOrder.Ascending;

    // Create SortDescription for City field
    SortDescription citySortDescription = new SortDescription(cityNameField);
    citySortDescription.CaseSensitivity = CaseSensitivity.Insensitive;
    citySortDescription.SortOrder = SortOrder.Ascending;

    // Create our TableSortDescription
    TableSortDescription tableSortDescription = new TableSortDescription(
      new List<SortDescription>() { countrySortDescription, citySortDescription });

    return worldCitiesTable.Sort(tableSortDescription);
  }
}

//var featSceneLayer = ...;
//var sname = featSceneLayer.Name;
await QueuedTask.Run(() =>
{
  if (!featSceneLayer.HasAssociatedFeatureService)
    return;//no search or select

  //Select all features within the current map view
  var sz = MapView.Active.GetViewSize();
  var map_pt1 = MapView.Active.ClientToMap(new System.Windows.Point(0, sz.Height));
  var map_pt2 = MapView.Active.ClientToMap(new System.Windows.Point(sz.Width, 0));

  //Convert to an envelope
  var temp_env = EnvelopeBuilderEx.CreateEnvelope(map_pt1, map_pt2, MapView.Active.Map.SpatialReference);

  //Project if needed to the layer spatial ref
  SpatialReference sr = null;
  using (var fc = featSceneLayer.GetFeatureClass())
  using (var fdef = fc.GetDefinition())
    sr = fdef.GetSpatialReference();

  var env = GeometryEngine.Instance.Project(temp_env, sr) as Envelope;

  //Set up a query filter
  var sf = new SpatialQueryFilter()
  {
    FilterGeometry = env,
    SpatialRelationship = SpatialRelationship.Intersects,
    SubFields = "*"
  };

  //Select against the feature service
  var select = featSceneLayer.Select(sf);
  if (select.GetCount() > 0)
  {
    //enumerate over the selected features
    using (var rc = select.Search())
    {
      while (rc.MoveNext())
      {
        using (var feature = rc.Current as Feature)
        {
          var oid = feature.GetObjectID();
          //etc.
        }
      }
    }
  }

  MapView.Active.Map.ClearSelection();

});