Вы можете l oop через все элементы tr , а затем найти указанный элемент c td из текущего элемента.
$('#datable_1 tr').each(function(index) {
console.log($(this).find('td:eq(8)').text());
});
$('#datable_1 tr').each(function(index) {
console.log($(this).find('td:eq(8)').text());
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table id="datable_1">
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
</table>
ИЛИ: С nth-child
:
$('#datable_1 tr td:nth-child(9)').each(function(index) {
console.log($(this).text());
});
$('#datable_1 tr td:nth-child(9)').each(function(index) {
console.log($(this).text());
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table id="datable_1">
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
</table>
Если целевой элемент всегда является последним дочерним элементом, то лучше использовать селектор :last-child
:
$('#datable_1 tr td:last-child').each(function(index) {
console.log($(this).text());
});
$('#datable_1 tr td:last-child').each(function(index) {
console.log($(this).text());
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table id="datable_1">
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
<tr>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td>lorem ipsum</td>
<td style="display:none;">I WANT TO GET THIS HIDDEN TEXT</td>
</tr>
</table>