Setting the sortable configuration for a Gantt column via TagHelpers does not enable sorting for the column.
Columns are not sorted.
When sorting is enabled for a column it should be sortable.
Set the sortable configuration for the desired columns after initialization of the Gantt component - REPL
$("document").ready(function(){
var gantt = $("#gantt").getKendoGantt();
var options = gantt.options;
options.autoBind = true;
options.columns[2].columns[0].sortable = true; //enable sorting for Start column
options.columns[2].columns[1].sortable = true; //enable sorting for End column
gantt.setOptions(options);
})