I have recently got a 2year old staffordshire bull terrier, who needs filling up what is the best food I can give him?

I don't know if this is the best dog food or not but when I had a German Shepard female would would constantly hoist herself over a 6' chain link fence and go terrorize the neighborhood I gave her peanut butter sandwiches. That put the weight on her in a hurry.

Some dogs will not start to fill out until they hit 2 years old so it may be a natural progression from now on anyway.
I have a skinny dog here who just turned 2 last week I am hoping now he will finally start filling out.

What food are you currently feeding? I have started mine on a mix of raw beef and lamb and after only a week I can already see an improvement. The mix I give is about 2/3 beef to 1/3 lamb flap, ground together. The lamb is very fatty, but it is considered a 'healthy' fat and is great for weight gain.
On top of that I still feed dry food so that he maintains a balanced diet rather than only feeding meat on its own but it has really been working for him.

You can also try just mixing some higher calorie foods in with his regular dog food, pasta is a good one.

And of course feeding a higher quality dog food will help as well. Cheaper brands tend to contain more fillers such as grains, while the more expensive brands contain a higher quantity of meats and nutritional ingredients. Just have a look at the ingredients on the back of the package, if the first ingredient listed is meat you are on to a winner.

Look for a food that lists a high quality source of protein as it's first and main ingredient. I like Blue Buffalo if you are in the US. Make sure she is up to date with worm and flea treatment, and plenty of exercise. Some dogs are naturally smaller, and with bully breeds such as yours it's usually not until their second year that they start filling out. Is she/he spayed/neutered? Altered dogs tend to pack on little extra weight, this is why it's so important to keep them exercised. A heavier dog tends to have issues with joints and ligaments. Remember to do the weight gain slowly and naturally. Once he starts feeling at "home" the stress will leave and weight will easily come.

I have a northern Inuit 23 weeks although he weighs 4 stone he is very thin I am feeding the Barf diet and have been giving him carbs such as pasta, potatoes, what else can I feed him to get him to fill out a bit.