Ok, I found it here:
/components/com_jem/views/event/tmpl/default.php
The following code is the one which shows the line, I don't want to have:
<dt class="category"><?php echo $n < 2 ? JText::_('COM_JEM_CATEGORY') : JText::_('COM_JEM_CATEGORIES'); ?>:</dt>
<dd class="category">
<?php
$i = 0;
foreach ((array)$this->categories as $category) :
?><a href="<?php echo JRoute::_(JemHelperRoute::getCategoryRoute($category->catslug)); ?>"><?php echo $this->escape($category->catname); ?></a><?php
$i++;
if ($i != $n) :
echo ', ';
endif;
endforeach;
?>
I have delete this, know it works.
JEM is great and I love it after a ew hours. Great job.
Thx,
ToKo