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();

});