Get ID from database when a specific td is clicked

Hi,
at first you MUST escape output data, e.g. html_escape($row->agenten) for string. For digits - (int)$row->projectid and use php native function rawurlencode for url's segment.

You can display row ID via bootstrap tooltip

foreach ($query->result() as $row_id => $row)
  ....
   echo "<td class=\"tootlip\" title=\"echo $row_id\"><a href='http://managementtool/index.php/Home/terugbel'>" . $row->terugbellen . "</td></a>";
  ....
}

Or may be I do not understand your question correctly?