I Picked Up A Friendly Stray Thin Emaciated Dog. He Was So Thin You Could See His Ribs Very Easy. Went To Vet He Said Need To Make His Stomach Swell Up Very Fast Like A Balloon. WHAT COULD GIVE THE DOG TO DO THIS?

That poor baby. There may have been a bit of a misunderstanding. Just feeding several small meals a day of a high quality diet should make the pup put on a lot of weight very quickly and is the best, safest and healthiest way to put on weight quickly for an emaciated dog.
His stomach probably doesn't hold much right now and trying to eat to much too fast may also lead to something like bloat. He also isn't in the best all around shape right now so feeding a bunch of things that aren't good for him may cause him some trouble more easily than if he was in better condition.
He definitely needs to eat and gain weight but also needs to be done in the safest and healthiest way possible. Feeding food that isn't good for them to put on weight quickly isn't really good either.
You could try feeding a puppy food for now, add some canned food or even speak to your vet about adding a little A/D or something but just smaller and  frequent meals will usually accomplish your goal quickly. You might also ask about making him up some satin balls (often used for dogs who need to gain a little before a show ect.) and giving a few a day in addition to a good diet. Ask a vet to help you set up a good feeding plan that is safe and will make him balloon up fast.
You might also speak to your vet about a broad spectrum deworming process just in case that also has something to do with the pups weight issues. He's a very lucky pup. Let us know how he's doing.
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Um, my dogs a jack russel and she was very thin because she chases birds,m and we were concerned about her, we took her to the vets and they gave us this food that makes them fat, I can't remember what it's called, but it worked.