<?php
    $args = array(
        'post_type' => 'produkty',
        'meta_key' => 'produkt_nowosc',
        'meta_value' => 'tak',
        'posts_per_page' => -1
    );

    $query = new WP_Query($args);
    $q = array();

    while ( $query->have_posts() ) {
        $query->the_post();
        $a = '<a href="'. get_permalink() .'">' . get_the_title() .'</a>';
        $terms = wp_get_post_terms( $post->ID, 'kategorie_produktow', $args );
        foreach ( $terms as $term) {
            $term_link = get_term_link( $term );
            $b = '<span>'.$term->name.'</span>';
        }
        $q[$b][] = $a;
    }
    wp_reset_postdata();
    foreach ($q as $key=>$values) {
        echo $key;
        echo '<ul>';
            foreach ($values as $value){
                echo '<li>' . $value . '</li>';
            }
        echo '</ul>';
    }
?>