Corrected

<!DOCTYPE html>
<html>
<body>

<input type="checkbox" id="_My.notFinal" onchange='hello()'>
<label><b>Buying for someone else.</b>
  <label>&nbsp;

    <span id="LicenseCustomer" style="display:none">

<tr valign=middle>
    <td class="bodycopy" align=right width=160><b>License Contact:</b>&nbsp;</td>
    <td class="smallcopy" nowrap><input name="_My.LicenseContact" type="text" class="inputBox" size="32" _label="<br>License Contact"></td>
    </tr>
    <tr valign=middle>
    <td class="bodycopy" align=right><b> License E-mail Address:</b>&nbsp;</td>
    <td class="smallcopy" nowrap><input name="_My.LicenseEmail" type="text" class="inputBox" size="32" _label="<br> License E-mail Address"></td>
    </tr>
    <tr valign=middle>
    <td class="bodycopy" align=right><b> License Phone:</b>&nbsp;</td>
    <td class="smallcopy" nowrap><input name="_My.LicensePhone" type="text" class="inputBox" size="32" _label="<br> License Phone"></td>
    </tr>

</span>


<script>
function hello() {

  var lfckv = document.getElementById("_My.notFinal").checked;

  if (lfckv) {

    document.getElementById("LicenseCustomer").style.display = "block";
  } else {

    document.getElementById("LicenseCustomer").style.display = "none";
  }
}
</script>

</body>
</html>