In magento if we need to get the custom options and their sub options of any product we need to write a query and from that result we can extract the options.

Lets see how can we do it:

Firstly, load the product from the catalog/product model with product id as:

$_item = Mage::getModel('catalog/product')->load($productId);

Now we have that product. To fetch the options collection from the product we will use the method getProductOptionCollection(), from the model 'catalog/product_option'.

 $options = Mage::getModel('catalog/product_option')->getProductOptionCollection($_item);

In the above query we have passed the product as parameter to function getProductOptionCollection(). Now, we have the list of custom options lets print them, for that follow the below code.

if(!empty($options))
{
     foreach ($options as  $option)
       {
        echo "Option :".$option->getDefaultTitle()."\n";
        echo "Values:\n";

           foreach ($option->getValues() as  $value)
           {
           print_r($value->getData());
           }
        }
 }

In the above code in foreach loop we have getDefaultTitle() method to fetch the option title and then in another nested loop printed each values of option.

In this way we can fetch the custom options of any product and perform any optrations on them.