in the second parameter 'this' in JQuery is an Object. On the server you have declared it as Page. You might need to change the server side code to accept Object.

I also believe that you might have to decorate the serverside method with

Code:
[WebMethod]
Public Shared........
Change your onclick event to call a JQuery function in the form....

Code:
$("#id").click(function (event) {
            $.ajax({
            url: rootDir + Page/Method',
            type: 'POST',
            dataType: 'json',
            data: { jsCodetoRun : "$('#basic-modal-ontent').modal()", Page: this }
            contentType: 'application/json; charset=utf-8',
            success: function (data) {
                alert(data);
            },
            error: function (data, textStatus, exceptionThrown) {
                alert(data.responseText);
            }

            });
        });