We can get custom attribute value of Customer in magento 2 by simple way. If we have created any customer attribute in Magento 2 and we need to get that value in any place in code you can just get custom attribute value by below way,
Let’s we consider Mobile attribute value is custom attribute value created for Customer, attribute code for Mobile is mobile.
You can get customer custom_attribute value by,
$customer = $CUSTOMER_OBJECT; // GET customer object
$customer->getCustomAttribute('mobile')->getValue();
return will be your customer custom_attribute mobile value.