Hola elabx,
thanks for your advice.
After some debugging, this code finally works:
<?php foreach($page->children() as $subpage): ?>
<h2><?php echo $subpage->publication_year ?></h2>
<?php foreach($subpage->Repeater_publication as $publication): ?>
<p><?php echo $publication->repeater_description ?></p>
<a href="<?php $publication->repeater_download->url ?>">Download</a>
<?php endforeach; ?>
<?php endforeach; ?>
My next goal is to create a real download link for pdf or doc files. And the link must be visible, if it's populated.
What I could't understand is, after creating such a template.php, do I have to tell Processwire somewhere, that this template exists?