get value and send in url using Ajax

Try again with code below:

$(document).ready(function () {
    $('#go').click(function() {
        $.get('Chess.php', { number: $('#nombre').val() } );
    });
});

PS: Its stranger the attribute value called nombre and the field called number. Change this too. Other tip is dont use Uppercase for the url, use only 'chess.php'.

I hope to help you.

There's a missing }) ...

Plus you have to add in the head section of your script the following :

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js" type="text/javascript"></script>

<script type="text/javascript">

$(document).ready(function () 
{
    $("#go").click(function() 
    {
        var n = document.getElementById('nombre').value;
        alert("Chess.php?number=9");
        $('#chess').load("Chess.php?number="+n);    
    })
});

</script>

it works now like this

$(document).ready(function () {
    $("#go").click(function() {
        $('#chess').load("Chess.php?number="+document.getElementById('nombre').value);
    });
});