How to get javascript slider to work! [closed]

You need to change the enqueueing part to this:

function skinsave_2016_slider() {
    wp_enqueue_script( 'skinsave_2016-slider-js', get_bloginfo( 'template_url' ) . '/js/slider-js.js', array(), null, true);
}
add_action('wp_enqueue_scripts', 'skinsave_2016_slider');

The problem was your function content_url() returns http://yourdomain.com/wp-content, and not the URL of the template. get_bloginfo( 'template_url' ) does return http://yourdomain.com/wp-content/themes/yourthemeslug.

The second version you tried you wrote bloginfo('skinsave_2016');, where ‘skinsave_2016’ is not a valid argument.

Stick with the first version though, because it is the right way.

Also be sure your theme calls wp_head() and wp_footer()!