Add popup on clicking on course button for non logged in users.

add_action('wp_footer','check_logged_in_and_form');
function check_logged_in_and_form(){
    global $post;
    $course_id = $post->ID;
    if(is_singular('course')){
       if((!is_user_logged_in()) || (is_user_logged_in() && function_exists('bp_course_is_member') && !bp_course_is_member($course_id,get_current_user_id()))){
            ?>
            <script>
            jQuery(document).ready(function($){
                $('a.course_button').on('click',function(event){
                  event.preventDefault();
                    $('.ajax-popup-link').trigger('click');
                });
            });
            </script>
            <?php
        } 
    }
}