public bool CanLookupSymbol()

//Note: Run within QueuedTask.Run
//Get the selection
var selection = featureLayer.GetSelection();
  //Get the first Object ID
  var firstOID = selection.GetObjectIDs().FirstOrDefault();
  //Determine whether the layer's renderer type supports symbol lookup.
  if (featureLayer.CanLookupSymbol())
  {
      //Looks up the symbol for the corresponding feature identified by the object id.
      var symbol = featureLayer.LookupSymbol(firstOID, MapView.Active);
      var jSon = symbol.ToJson(); //Create a JSON encoding of the symbol
      //Do something with symbol
  }