$servername = "localhost";
$username = "root";
$password = "";
$dbname = "tesddddt";

$conn = mysqli_connect($servername, $username, $password, $dbname);
mysqli_set_charset($conn,"utf8");

if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
$sql = "SELECT * FROM customer";
$result = mysqli_query($conn, $sql);

if (mysqli_num_rows($result) > 0) {
    // output data of each row
    while($row = mysqli_fetch_assoc($result)) {
        echo "id: " . $row["uid"]. " - Name: " . $row["username"]. " " . $row["email"]. "<br>";
    }
} else {
    echo "0 results";
}

public function __construct(){
    try {

        $conn = new PDO("mysql:host=$this->db_host;dbname=$this->db_name", $this->db_user_name, $this->db_pass);
        mysqli_set_charset($conn,"utf8"); // <- added here
        $this->conn=$conn;
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    }
    catch(PDOException $e)
    {
        echo "Connection failed: " . $e->getMessage();
    }
}

Warning: mysqli_set_charset() expects parameter 1 to be mysqli, object given in...

$conn = new PDO("mysql:host=yourhost;dbname=yourdbname;charset=utf8");

header("Content-Type: text/html; charset=utf-8");
//header("Content-Type: text/html; charset=utf-8_general_ci");
//error_reporting(E_ALL);
ini_set('display_errors', true);
set_time_limit(480);
define("DSN", "mysql:host=localhost;dbname=biblewheel");