FacetWP + Co-Authors Plus

gistfile1.php

<?php

$args = array(
    'posts_per_page' => -1,
    'post_type' => 'bookshelf',
    'post_status' => 'publish',
    'tax_query' => array( // Query on the "Co-Authors Plus" custom taxonomy
        array(
            'taxonomy' => 'author',
            'terms' => $author // the author ID
        )
    )
);

// The Query
$the_query = new WP_Query( $args );

// The Loop
if ( $the_query->have_posts() ) {
    echo '<div class="masonry-item"><h2>Bookshelf</h2>';
    echo '<ul>';
    while ( $the_query->have_posts() ) {
        $the_query->the_post();
        echo '<li>';
        echo '<a href="'.get_permalink().'">'.get_the_title().'</a>';
        echo '</li>';
    }
    echo '</ul></div>';
}

wp_reset_postdata();