@(Html.Kendo().ListBox()
              .Name("PositionsDatasource")
              .DataValueField("Id")
              .DataTextField("Name")
              .Toolbar(toolbar =>
              {
                  toolbar.Position(Kendo.Mvc.UI.Fluent.ListBoxToolbarPosition.Right);
                  toolbar.Tools(tools => tools
                      .TransferTo()
                      .TransferFrom()
                      .TransferAllTo()
                      .TransferAllFrom()
                      );
              })
              .DataSource(datasource => datasource
                      .Custom()
                      .Transport(transport => transport
                          .Read(read => read.Action("GetPositions", "Process"))))
              .ConnectWith("PositionsSelected")
              .DropSources("PositionsSelected")
              .Draggable(true)
              .Navigatable(true)
              .Selectable(ListBoxSelectable.Single)
              .Events(events => events
                  .Add("onAdd")
                  .Remove("onRemove"))
              )
        
        @(Html.Kendo().ListBox()
                      .Name("PositionsSelected")
                      .DataValueField("Id")
                      .DataTextField("Name")
                      .BindTo(Model.Positions)
                      .ConnectWith("PositionsDatasource")
                      .DropSources("PositionsDatasource")
                      .Draggable(true)
                      .Navigatable(true)
                      .Selectable(ListBoxSelectable.Single)
                      .Events(events => events
                      .Add("onAdd")
                      .Remove("onRemove"))
                      )

    function onAdd(e) {

        debugger;

        var model = @Html.Raw(Json.Encode(Model));

        e.preventDefault();

        var listBoxName = getListBoxName(e);

        if (listBoxName === "PositionsSelected") {

            for (var index = 0; index < e.dataItems.length; index++) {

                var dataItem = e.dataItems[index];

здесь думал обновлять модель Model.Positions.Add(new PositionComboBoxItem() {Id = dataItem.Id, Name = dataItem.Name })

            }
        }
        // alert("add : " + getListBoxName(e) + " : " + e.dataItems.length + " item(s)");
    }