To create modal dialogs on dashboard single pages in packages, the following steps are necessary (assuming the package already exists):

Creating the following supplementary files / folders (for sake of readability):

/my_package/controllers/dialog/my_dialog.php
/my_package/views/dialogs/my_dialog.php

The 'my_dialog' controller should look like this:

namespace Concrete\Package\MyPackage\Controller\Dialog;

use Concrete\Core\Controller\Controller;

class MyDialog extends Controller
{
    protected $viewPath = 'dialogs/my_dialog';

    public function view()
    {
        /** your code */
    }
}

The 'my_dialog' view is a standard Concrete5 view.

Add (if not exists) the following method inside the package controller:

public function on_start()
{
    Route::register('/my_package/my_dialog',
    '\Concrete\Package\MyPackage\Controller\Dialog\MyDialog::view');
}

Now in the single page view:

My dialog

 $('a[data-button=add-event]').on('click', function() {
        $.fn.dialog.open({
            href: '',
            title: 'My dialog',
            width: '280',
            height: '220',
            modal: true
        });
        return false;
    });