This code recipe would move the Email address to the top of the checkout page before other fields

my_pmpro_email_address_first_on_checkout.php

<?php // Do not Copy This Line

/**
 * Add the following code to your PMPro Customizations Plugin - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function pmpro_move_name_fields() {
	global $pmpro_pages;
		if(is_page($pmpro_pages['checkout'])) {
		?>
		<script>
			jQuery( '.pmpro_checkout-field-bemail' ).prependTo( '.pmpro_checkout-field-username' );
		</script>
		<?php
		}
}
add_action( 'wp_footer', 'pmpro_move_name_fields' );