checkbox based input item

It's because ID value should only be used once.

Change it to class="chb" and getElementsByClassName('chb') and it should work as intended.

I try this . not working
echo '<td  align="center"><input type="number" min="0" max="999" name="cnt" value="0"   onkeyup="sum();" class="texttwo" disabled></td>';                 

                     echo '<td align="center"><input type="checkbox" value="' . $row['certificate_id'] . '" name="certid[]" class="chb"></td>';  



<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
  document.getElementsByClassName('chb').onchange = function() {
    document.getElementsByClassName('texttwo').disabled = !this.checked;
};
</script>