Without knowing the actual scenario... I am assuming your goal is actually to get the dynamically added items either by iterating over them or something else...
Any dynamically added DOM element that is done on the client side using JavaScript / jQuery, will not be reflected automatically to the server side. You will need to serialize them in a different way and push them back to the server side during postback. One way you can do this is by serializing all the Options of the Select element in a hidden input. You can mark the hidden input as runat=server if you wish to make it easier for you to access, otherwise use Request.Form["...hidden input NAME attribute here... NOT ID..."] to get the value out. After you get it, you can do whatever you want with the values.
I imagine your hidden input should have some value like: "1:First Value,2:Second Value,3:...". Just do some string manipulation to split them up and iterate over them.
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