.Events(e => e.DataBound("setRequiredAttr"))
... 
        function setRequiredAttr(e) {
            if (e.sender.value()) {
                e.sender.element.removeAttr("required");
            }
            else {
                e.sender.element.attr("required", "required");
            }
        }

//The Grid's toolbar    
.ToolBar(x =>
        {
            x.Template("<a class='k-button k-button-icontext' onclick='customCommand()' href='#'></span>Validate DDL</a>");
        })
..
//The button click handler
        function customCommand() {
            var validator = $("#myForm").kendoValidator().data('kendoValidator');
            validator.validate();

            if (validator.validate()) {
            $("#result").text("");
        } else {
            $("#result").text("Choose a value from the list");
        }
        }
...
//The DropDownList declaration
<form id="myForm" action="someAction" method="post">
    @(Html.Kendo().DropDownList()
          .Name("color")
          .OptionLabel("Select item")
          .DataTextField("Text")
          .DataValueField("Value")
          .BindTo(new List<SelectListItem>() {
              new SelectListItem() {
                  Text = "Black",
                  Value = "1"
              },
              new SelectListItem() {
                  Text = "Orange",
                  Value = "2"
              }
          })
          .Events(e => e.DataBound("setRequiredAttr"))
          .HtmlAttributes(new { style = "width: 15%" })
    )
</form>
<div id="result"></div>