Your query would be something like:
$post_ids = $wpdb->get_col( "SELECT DISTINCT post_id FROM {$wpdb->prefix}wti_like_post WHERE user_id = {$author->ID}" );
Then you can pass that array of post IDs as the post__in
argument of WP_Query
:
$args = array(
'posts_per_page' => -1,
'post__in' => $post_ids
);