How to insert a text in all pages and posts before or after specific places?

You can add to before or after the content as well in a similar fashion. I use this code:

function rt_before_after($content) {
    $beforecontent="This goes before the content.";
    $aftercontent="And this will come after.";
    $fullcontent = $beforecontent . $content . $aftercontent;

    return $fullcontent;
}
add_filter('the_content', 'rt_before_after');

You could use it similarly with the_title,.

The reko_hook() you have likely came with your theme or a different plugin.