After several days, finally I found how to make ajax call from my wordpress site, I hope that it will help those who have had this problem:

first, I was created a post inside a wordpress whit this html code:

<section id="main">
    <table id="tng" class="datagrid">
    	<thead><tr><th colspan="3"> 
            Sample ping App
            </th>
        </thead>
        <tbody>
    	</tr><tr>
    		<td width="50%" align="right"><b>Host or IP:</b></td>
    		<td><input  id="ip" size="20" value="" ></td>
                <td><button type="button" onclick="PING()">Ping</button></td>
    	</tr>
        </tbody>
    </table>
    <img id="image" src="spinner.gif" alt="wait..." style="display: none;">
    <br>
    
</section>	
<section id=food>
	<h3 id="notification"></h3>
</section>

As you can see the only important thing is the onclick event for the button that calls de functionPING()