You can't have two elements with the same ID attribute. You'll need to use class instead
<script type="text/javascript">
$(document).ready(function() {
//toggle `popup` / `inline` mode
$.fn.editable.defaults.mode = 'popup';
$('.confirm_assistance').editable({
url: '/post'
});
});
</script>
<tr class="gradeA">
<td>Pepa Loraine</td>
<td>No</td>
<td>25</td>
<td></td>
<td></td>
<td>1825€</td>
<td>250.00€</td>
<td>0.00€</td>
<td>1575.00€</td>
<td><a href="#" class="confirm_assistance" data-type="text" data-placement="right" data-title="Enter username" data-pk="22">0</a></td>
<td>2014-05-13 00:29:29</td>
<td>Ibiza Rent a Car </td>
</tr>
<tr class="gradeA">
<td>Pepa Loraine</td>
<td>No</td>
<td>25</td>
<td></td>
<td></td>
<td>1825€</td>
<td>250.00€</td>
<td>0.00€</td>
<td>1575.00€</td>
<td><a href="#" class="confirm_assistance" data-type="text" data-placement="right" data-title="Enter username" data-pk="30">0</a></td>
<td>2014-05-13 00:30:14</td>
<td>Juan Del Árbol</td>
</tr>