Getting it into the diet is a great question. Many food sources of C aren’t digestible to a carnivore. Dr. Wendell used ascorbates for better absorption.
This is from another article discussing that:
Vitamin C Dosage for Dogs
The average dog normally produces about 18 milligrams of vitamin C per pound of body weight per day. Therefore, for a dog that is free of clinically significant symptoms but is experiencing unusual stress, supplementation with about that much C per day appears be a conservative maintenance dosage. (About 500 milligrams for a 28-lb. dog daily.) To increase absorption, veterinarians recommend splitting the total daily dosage into several feedings during the day.
However, many holistic veterinarians routinely suggest maintenance doses that are three to four times that amount. They explain that modern, domestic dogs need more vitamin C than the theoretical “natural” dog, since their bodies must deal with so many challenges: stress, pollution, chemicals and pesticides, and poor diets, to name a few.
Too much vitamin C, especially if given in one dose, will cause diarrhea in dogs. What amount is too much varies from dog to dog, so, when administering the maximum amount of C for a therapeutic (not just maintenance) dose, many veterinarians will suggest that you increase the dose in 100-500 milligram-per-day increments until the dog develops diarrhea, then reduce his daily dose to the previous day’s dose. (This is often referred to as dosing to “bowel tolerance.”)
There’s also a lot more info in that article. Here’s the link:
https://www.whole-dog-journal.com/food/benefits-of-vitamin-c-to-your-dog/
