function fancybox_init()
{
    wp_register_script('fancybox', plugins_url('/cennik/public/js/cennik.js', __FILE__), array('jquery'));
    wp_enqueue_script('fancybox');
}

add_action('wp_enqueue_scripts', 'fancybox_init');

$(window).ready(function(){
    alert("asd");
});

$(window).ready(function(){
    alert("asd");
});

jQuery( document ).ready(function() {
    alert("asd");
});