Hello,
Is there a way to make veronika display popular city of published ads at the footer

You have this in footer.php:
      <div class="location">
        <?php $regions = RegionStats::newInstance()->listRegions('%%%%', '>', 'i_num_items DESC'); ?>
        <?php $i = 1; ?>
        <?php foreach($regions as $r) { ?>
          <?php if($i <= 12) { ?>
            <span class="region-span"><a href="<?php echo osc_search_url(array('page' => 'search', 'sRegion' => $r['pk_i_id']));?>"><?php echo $r['s_name']; ?></a></span>
            <?php $i++; ?>
          <?php } ?>
        <?php } ?>
      </div>

You may try to change it into:
      <div class="location">
        <?php $regions = CityStats::newInstance()->listCities('%%%%', '>', 'i_num_items DESC'); ?>
        <?php $i = 1; ?>
        <?php foreach($regions as $r) { ?>
          <?php if($i <= 12) { ?>
            <span class="region-span"><a href="<?php echo osc_search_url(array('page' => 'search', 'sCity' => $r['pk_i_id']));?>"><?php echo $r['s_name']; ?></a></span>
            <?php $i++; ?>
          <?php } ?>
        <?php } ?>
      </div>

But I would say some adjustments may be required

I changed it but no city displayed at footer. What adjustment do i need to make

Check CityStats on it's functions and how to use them.

Pls dont be annoyed. Where can i get details of how to use it. So i can read and do accordingly

This class is in oc-includes/osclass/classes

Ok thank you