\Bitrix\Main\Loader::includeModule('sale');
$orderId = 1;
$order = \Bitrix\Sale\Order::load($orderId);
$shipmentCollection = $order->getShipmentCollection();
foreach($shipmentCollection as $shipment) {
if($shipment->isSystem()) {
continue;
}
$trackingNumber = $shipment->getField('TRACKING_NUMBER');
}