Get text of td via element num.

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table>
<tr>
  <td class="trade-num">100</td>
</tr>
<tr>
  <td class="trade-num">101</td>
</tr>
<tr>
  <td class="trade-num">102</td>
</tr>
<tr>
  <td class="trade-num">103</td>
</tr>
<tr>
  <td class="trade-num">104</td>
</tr>
<tr>
  <td class="trade-num">105</td>
</tr>
</table>

JavaScript

var tradeNumEl = $("td.trade-num").length - 2;
console.log($("td.trade-num")[tradeNumEl].text() );