To make an AJAX call to a controller action in a CakePHP application, you can use the $.ajax function provided by jQuery. Here’s an example of how you can make an AJAX call to a controller action:

1. Add a route for the controller action: First, you will need to add a route for the controller action you want to call in your application’s config/routes.php file. For example, to call the getData action in the Users controller, you can add the following route:

Router::connect('/users/get-data', ['controller' => 'Users', 'action' => 'getData']);

2. Create the controller action: Next, you will need to create the getData action in the Users controller. The action should return the data you want to pass back to the AJAX call. For example:

class UsersController extends AppController {
  public function getData() {
    $data = ['key' => 'value'];
    $this->set(compact('data'));
    $this->set('_serialize', 'data');
  }
}

3. Make the AJAX call: Finally, you can use the $.ajax function to make the AJAX call to the getData action. For example:

$.ajax({
  url: '/users/get-data',
  type: 'GET',
  success: function(data) {
    console.log(data);
  }
});

This will make an HTTP GET request to the /users/get-data URL, which will trigger the getData action in the Users controller. The data returned by the action will be passed to the success callback function.

Note: This is just a basic example of how to make an AJAX call to a controller action in CakePHP. You can customize the AJAX call and the controller action to meet the specific needs of your application.