<?php
if (!empty($_GET['msg'])) {

    global $wpdb;
    $user_id = $_GET['id'];
    $sql = $wpdb->prepare("SELECT * FROM wp_quiz WHERE quiz_id='%d'", $user_id);
    $result = $wpdb->get_row($sql, ARRAY_A);
    var_dump($user_id);
    var_dump($result);

    $total = $result['total_count'];