public void Split( 
   SelectionSet features,
   Geometry splitGeometry
)

var select = MapView.Active.SelectFeatures(clipPoly);

var cutFeatures = new EditOperation();
cutFeatures.Name = "Cut Features";
cutFeatures.Split(featureLayer, oid, cutLine);

//Cut all the selected features in the active view
//Select using a polygon (for example)
//at 2.x - var kvps = MapView.Active.SelectFeatures(polygon).Select(
//      k => new KeyValuePair<MapMember, List<long>>(k.Key as MapMember, k.Value));
//cutFeatures.Split(kvps, cutLine);
var sset = MapView.Active.SelectFeatures(polygon);
cutFeatures.Split(sset, cutLine);

//Execute to execute the operation
//Must be called within QueuedTask.Run
cutFeatures.Execute();

//or use async flavor
//await cutFeatures.ExecuteAsync();