$(document).ready(function () {
    $('.drag').on("mouseover", function () {
        AfterPostBack();
        $(this).draggable()
          .click( function () {
              $(this).draggable({ disabled: false });
          }).dblclick( function () {
              $(this).draggable({ disabled: true });
          });
    });
    $('.text_label').on("blur",function () {

        $(this).removeClass('focus');
    });
});

var AfterPostBack = function () {
  $('.drag').draggable("option", "containment", 'parent');
  $('.drag').draggable("option", "snap", 'parent');
   $('.drag').draggable("option", "cursor", 'move');
 };

<script type="text/javascript" src="Scripts/jquery-1.8.0.min.js"></script>
<script type="text/javascript" src="Scripts/jquery-ui-1.8.23.custom.min.js"></script>
<script type="text/javascript" src="Scripts/myplugin.js"></script>
<link href="Styles/myplugin.css" rel="stylesheet" type="text/css" />

<asp:UpdatePanel runat="server" ID="UP1" UpdateMode="Conditional" ChildrenAsTriggers="false">
<ContentTemplate>
 <asp:Button ID="btn_AddText" runat="server" Text="Add Text" OnClick="AddText" />
<asp:PlaceHolder ID="ph1" runat="server">
    <div class="drag">
        <asp:Label ID="lbl1" class="text_label" runat="server" Text="Click Me"/>
     </div>
</asp:PlaceHolder>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="btn_AddText" EventName="Click" />
</Triggers>
</asp:UpdatePanel>

Sys.Application.add_init(function () {
        // Initialization code here, meant to run once.
        try {
            //doOnes();
            doAllways();
        } catch (e) {
            console.log('Sys.Application.add_init: ', e);
        }
});

$(document).ready(function () {
  console.log('document.ready');
  //doAllways();
}

function pageLoad() {
  console.log('pageLoad');
  //doAftrerAjax();
  doAllways();
}

function doOnes() {
  console.log(doOnes);
}

function doAftrerAjax() {
  console.log('pageLoad');
}

function doAllways(){
  console.log('doAftrerAjax
  AfterPostBack();             <---this the place for the code
}