apply_filters ( 'jetpack_relatedposts_filter_post_link_rel', string $link_rel, int $post->ID )

Notes

You can use this filter to disable the nofollow attribute that’s added to Related Posts by default. To do so, use the following snippet:

function jeherve_custom_rp_rel( $rel, $post_id ) {
    return '';
}
add_filter( 'jetpack_relatedposts_filter_post_link_rel', 'jeherve_custom_rp_rel', 20, 2 );