Proiect

<script type="text/javascript" src="https://code.jquery.com/jquery-3.3.1.min.js"></script>

<table id="produse">
    <tr>
      <th width="20%">Produs</th>
      <th width="10%">Cantitate</th>
    </tr>
    <tr id="0">
      <td contenteditable="true">Produs</td><td contenteditable="true">0</td>
    </tr>
    <tr><td></td><td><input id="add" type="button" value="Add" style="float: right;" /></td></tr>
</table>
<style>
table#produse {
    width: 30%;
    background: repeat;
    border: 1px solid;
}

table#produse tr td[contenteditable="true"] {
  border: 1px solid #000;
}
</style>

<script type="text/javascript">
$(document).on("click", "#add", function() {
  var table = document.getElementById('produse'),
      count = $('tr[id]', table).attr('id');
  var row = '<tr id="'+ count+1 +'"><td contenteditable="true">Nume Produs</td><td contenteditable="true">Cantitate</td></tr>';
  $('tr[id]:last', table).after(row);
});
</script>