ColumnMenuInit

<div id="grid"></div>
<script>
$("#grid").kendoGrid({
  columns: [
    { field: "name" },
    { field: "age" },
  ],
  dataSource: [
    { name: "Jane Doe", age: 30},
    { name: "John Doe", age: 33}
  ],
  columnMenu: true,
  columnMenuInit: function(e) {
    var menu = e.container.find(".k-menu").data("kendoMenu");
    var field = e.field;
    menu.append({ text: "Custom" });
    menu.bind("select", function(e) {
      if ($(e.item).text() == "Custom") {
/* The result can be observed in the DevTools(F12) console of the browser. */
        console.log("Custom button for", field);
      }
    });
  }
});
</script>

<div id="grid"></div>
<script>
function grid_columnMenuInit(e) {
  var menu = e.container.find(".k-menu").data("kendoMenu");
  var field = e.field;
  menu.append({ text: "Custom" });
  menu.bind("select", function(e) {
    if ($(e.item).text() == "Custom") {
/* The result can be observed in the DevTools(F12) console of the browser. */
      console.log("Custom button for", field);
    }
  });
}
$("#grid").kendoGrid({
  columns: [
    { field: "name" },
    { field: "age" },
  ],
  dataSource: [
    { name: "Jane Doe", age: 30},
    { name: "John Doe", age: 33}
  ],
  columnMenu: true
});
var grid = $("#grid").data("kendoGrid");
grid.bind("columnMenuInit", grid_columnMenuInit);
</script>