mypmpro-append-content-infowindow-protected.php

<?php
/**
 * This recipe will display custom content in the marker info window. Members will need
 * a membership level of 1 or 2 in order for this to be displayed.
 *
 * 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 mypmpromm_single_marker_content_protected( $content, $member ){

	if( pmpro_hasMembershipLevel( 1, 2 ) ){ //Change levels to your preference
		
		$graduation_year = get_user_meta( $member['ID'], 'graduation_year', true );

		$content .= "<p><strong>Graduation Year</strong> ".$graduation_year."</p>";

	}

	return $content;
	
}
add_filter( 'pmpromm_single_marker_content', 'mypmpromm_single_marker_content_protected', 10, 2 );

This recipe is included in the blog post on "Adding Custom Content To Your Marker Info Window" at Paid Memberships Pro here: https://www.paidmembershipspro.com/adding-custom-content-to-your-marker-info-window/