JSFiddle - React, Tailwind, and code Playground

HTML

<table id="tbTitulars">
    <tr><td data-network="YT">un dato</td>
      <td data-network="FB"></td>
     <td data-network="CR">un dato</td></tr>
</table>

JavaScript

var clone = $("#tbTitulars tr:first").clone();

clone.find('td[data-network]').each(function(){
    if( $.trim( $(this).text() ) == '' ){
        $(this).text('Valor por defecto');
    }
});

$("#tbTitulars").append(clone);