jetpack_development_mode.php

<?php
/**
 * @package   Wordpress JetPack Theme Hooks
 * @author    jwwicks
 * @copyright Copyright (C) 2017 jwwicks
 * @license   GNU/GPLv2 and later
 *
 * http://www.gnu.org/licenses/gpl-2.0.html
 *
 * Note: Place the code below in your functions.php theme file
 */

/**
 * Enable JetPack Development mode selectively based on subdomain
 *
 * www.domain.com - production mode
 * develop.domain.com - development mode
 * staging.domain.com - development mode
 *
 */
if(!function_exists('onEnableJetPackDevelopmentMode')){
    function onEnableJetPackDevelopmentMode($is_development_mode){
        $parts = explode('.', $_SERVER['SERVER_NAME']);
        /* Assumes www.domain.com format
           adjust array as needed below to suit your setup
        */
        if(in_array($parts[0], array('develop', 'staging'))){
            $is_development_mode = true;
        }
        
        return $is_development_mode;
    }
}
add_filter('jetpack_development_mode', 'onEnableJetPackDevelopmentMode', 10, 1);