Topic: HOW TO USE JQYERY SELECT2 IN DROPDOWN

Step 1: Download relevant jQuery Select 2 files from jquery.com

Step2: Place the jQuery file in includes/page/footer.inc

Step3: Place the following code in company/0/js_cache/utils.js

$.fn.select2.amd.require([
    "select2/core",
    "select2/utils",
    "select2/compat/matcher"
    ], function (Select2, Utils, oldMatcher) {
        var $basicSingle = $(".js-example-basic-single");
        $.fn.select2.defaults.set("width", "100%");
        $basicSingle.select2();
    }
);

Re: HOW TO USE JQYERY SELECT2 IN DROPDOWN

Do not write to js_cache/utils.js as it will get overwritten on cache refresh when some settings change. The file js/utils.js is what you will want to change.

What is the context of your post?

jQuery is not used in FA core and in the standard themes. The dashboard_theme and exclusive_db themes use jQuery v1.3.2 in the themes' js folder.