short code in dialog

The user must be logged in for that shortcode to function. If you wanted to display the user’s email, you could do that with a couple of hooks.

The wpmem_post_register_data action comes after the user is registered. All registration data is available to this action in an array. You could globalize that array so that you could pick it up again later in the message.

The message that is displayed can be filtered with the wpmem_msg_dialog filter. If you globablize the array as mentioned, then you could pick up the global in this filter and the email (or any registration data) would be available for display.