This should do the trick:
var d = $(this).attr("data-datac");
Also, you need to change your HTML to give each element a seperate id. But it can be a tedious task to bind click events for a number of different ids. So i'd bind it to a seperate class. For example:
HTML
Javascript
$(".dateChanger").click(function () {
var d = $(this).attr("data-datac");
alert(d);
});