Javascript not working?

The “Failed to load resource” is probably a red herring and isn’t related to your issue. The fact that it is throwing an error about the $ shortcut means your js file is being loaded correctly.

The likely issue is that jQuery in WordPress loads in “noConflict” mode. As such the $ shortcut will not work by default. Try replacing your script with this:

<script type="text/javascript">
    jQuery(".menu-button").click(function () {
        jQuery(this).parents(".wrapper").toggleClass("show-menu");
    });
</script>

Or, alternatively if you really like the $ shortcut:

<script type="text/javascript">
    (function($) {
        $(".menu-button").click(function () {
            $(this).parents(".wrapper").toggleClass("show-menu");
        });
    })(jQuery);
</script>

There is also an issue with the logic in your javascript. The line

$(this).parents(".wrapper").toggleClass("show-menu");

Will not work as expected. jQuery.parents() returns a set of results while jQuery.toggleClass() expects a single element. If you know that the element directly above show-menu will always be wrapper and that is the only element you wish to effect, then you can simply swap that line out for this

$(this).parent(".wrapper").toggleClass("show-menu");

Alternatively, if wrapper can be an arbitrary height above show-menu, you will need something like this

<script type="text/javascript">
    jQuery(".menu-button").click(function () {
        jQuery(this).parents(".wrapper").each(function(){
            jQuery(this).toggleClass("show-menu");
        });
    });
</script>

Incidentally, the reason you are getting that “Not Found” error is because transitions.js does not exist at this url: https://generation-co.co/wp-content/themes/twentyfifteenG-CHILD/js/transition.js