JQuery datepicker not working after ajax call

You need to reinitialize the date picker in Ajax success

$('.datepicker').datepicker({dateFormat: "dd-mm-yy"});

$('#btn').click(function() {
    $.ajax({
        type: "GET",
        url: "my_ajax_stuff.php" ,
        success: function(response) {

            $('#ct').html(response);
            $( "#datepicker" ).datepicker();
            /*added following line to solve this issue ..but not worked*/
            //$( ".datepicker" ).datepicker({dateFormat: "dd-mm-yy"});

        } ,
        error: function () {
            $('#ct').html("Some problem fetching data.Please try again");
        }
    });
});

The answer you are looking for may be similar to this question: jQuery datepicker won't work on a AJAX added html element

You're replacing the datepicker element in the DOM with the ajax response. The reason this works for the first time is that PHP renders the my_ajax_stuff.php on first load already in the HTML so it becomes available to jQuery in the DOM.

// do this once the DOM's available...
$(function(){

// this line will add an event handler to the selected inputs, both
// current and future, whenever they are clicked...
// this is delegation at work, and you can use any containing element
// you like - I just used the "body" tag for convenience...
    $("body").on("click", ".datepicker", function(){
            $(this).datepicker();
            $(this).datepicker("show");
    });
});