JSFiddle - React, Tailwind, and code Playground

HTML

<fieldset id="fieldset">
    <legend id="legend">Professional development</legend>
    <div id="placeholder">
        <div id="template">
            <p>Item <input type ="text" size="25" name="prof_item" /><br /></p>
            <p>Duration <input type ="text" size="25" name="prof_duration" /><br /></p>
            <p>Enlargement <label for="enlargement"></label></p>
            <p><textarea name="prof_enlargement" cols="71" rows="5" id=""></textarea></p>
        </div> <!-- template -->
    </div> <!-- placeholder -->
    <p><button type="button" name="Submit" onclick="Add();">Add new item</button></p>
</fieldset>

JavaScript

var _counter = 0;
function Add() {
    _counter++;
    var oClone = document.getElementById("template").cloneNode(true);
    oClone.id += (_counter + "");
    document.getElementById("placeholder").appendChild(oClone);
}