The external website spits proper JSON and the code is too simple I don't know what can be wrong. I tried with get and post.
$(document).ready(function() {
$.get("https://www.w3schools.com/jquery/demo_ajax_json.js", function(result) {
alert(result);
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>