I am working on magento2 and i am try to access product all custom option. For now i have added to text box and for access custom option bellow code i have use.
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$product = $objectManager->get('Magento\Catalog\Model\Product')->load(1001);
$productOption = $product->getOptions();
foreach($productOption as $op)
{
echo "<pre>";
print_r($op);
die;
}