This recipe add user meta as email variables that may be used for the PMPro Email Template Editor Add On.

my-pmpro-email-data.php

<?php
/**
 * This recipe add user meta as email variables that may be used for
 * the PMPro Email Template Editor Add On.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_email_data( $data, $email ) {
	if ( ! empty( $data['user_login'] ) ) {
		$user = get_user_by( 'login', $data['user_login'] );

		if ( ! empty( $user ) && ! empty( $user->ID ) ) {
			$data['first_name'] = get_user_meta( $user->ID, 'first_name', true );
		}

		if ( ! empty( $user ) && ! empty( $user->ID ) ) {
			$data['prefix'] = get_user_meta( $user->ID, 'prefix', true );
		}
	}
	return $data;
}
add_filter( 'pmpro_email_data', 'my_pmpro_email_data', 10, 2 );