Question

view to controller method

        .ClientEvents(events =>
        {
            events.OnDataBinding("onDB");
        })

Answer 1

As dbaseman said – the insert operation sends the form values which will be used to generate new record with new datakey.
Also the name of the parameter by default is called id – in the update action method you could retrieve it like this:

[GridAction]
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Update(string id)
{
    // code..
    return View();
}