First of all, make sure you are using a good browser with debugging capabilities (I prefer Chrome), because you'll need it.
Secondly, I usually use the $.ajax request, instead of the post. Mainly because post is a wrapper around ajax and you can more finely change the settings of ajax.
type: 'POST', // Make sure you post
dataType: 'json', // Use this so that you request json from the server
url: "/sitioweb/json/",
data: data,
success: function(data) {
// The data that is returned is your json data, already parser, so you don't have to parse it!
alert(data.array[0]); // Need to write "array" because that is what you are sending to the browser (your structure looks like that, check what the server is responding with)
},
error: function(xhr, textStatus, errorThrown) {
console.log('AJAX communication failed:', textStatus, errorThrown); // In case there is an error (for example a 500)
}