function CheckSettings() {

$.ajax({
   type: 'POST',
   url: 'urlforsettingsphp',
   data: form_data,
   success: function(data)
   {
      $("#settings").html(data);
   }
});
}
CheckSettings();

$( document ).ready(function() {
$("#newlogintext").on("keyup", function(){
alert("test");
});

<div class="settings">
<b> General Settings </b>
<br>
<p>New login:</p> <input id="newlogintext" type="text" name="newlogin" />
</div>