You never enqueued the ajax_init in a function. Also you can use plugins_url() and split into two functions with a shortcode, like this:
(not tested)
<?php
/*
Plugin Name: Ajax Plugin
Description: Plugin for adding ajax
Version: 1.0
*/
/*-------------------------------------------------------*/
/* Register Scripts
/*-------------------------------------------------------*/
add_action( 'wp_enqueue_scripts', 'ajaxp_init' );
function ajaxp_init(){
/*
* registro del script
*/
wp_enqueue_script('jquery');
wp_register_script( 'jfile_general_js', plugins_url('pablowishlist.js', __FILE__));
wp_enqueue_script('jfile_general_js')
}
/*-------------------------------------------------------*/
/* Add shortcode
/*-------------------------------------------------------*/
add_shortcode('ajaxplug','jfile_manager');
function jfile_manager() {
global $post;
wp_localize_script('jquery_no_conflict','MyAjax', array(
'postId' => $post->ID,
'action' => 'ajaxp_add_wishlist'
));
}