JSFiddle - React, Tailwind, and code Playground

HTML

<table width="80%" cellspacing="0" cellpadding="0" >
  <th scope="col">Data</th>
       <tr>
         <td width="20%"><a href="#" class ="show_data_link">Show Data</a>
           <span class="data" value="5">1 </span>
          </td>
      </tr>
 </table>

JavaScript

$('.show_data_link').bind('click', function(){
    //returns the first class
    alert($(this).next().val());
    //retrns null
    //alert($('.data').next().html());
    //returns null
   // alert($('.data').closest().html());
  return false;
});