My moms dog is a walking bag of bones we have tried everything we no.He is very hipper and never seems sick.He just can't gain weight no matter what. Does anyone have anu suggestions to maybe but some meat on his bones?

First of all you need to have a stool sample checked for worms, the main reason for a very thin dog.
But some dogs are naturally very thin, such as the greyhounds, whippets, and I even had a very thin golden retriever LOL, who ate delicately and not a lot.

First of all how old is he? What breed is he? Has he always been thin or has he lost weight and just can't seem to gain it back? What is his normal diet? I agree that taking a stool sample in to the vet to check is a good place to start. IF parasites are the culprit, knowing which ones is a plus when it comes to treating the problem. And has he had regular vet care with no obvious problems in the past?
We can only guess, it could be something else entirely. But a good check up may be in his best interest if you think that he is unusually thin.

I would also like some answers to the above questions.

If all is well health wise then there are some options but I wouldn't like to go recommending diet before we know about the health of the dog.

Age also plays a big part, especially in younger dogs.
I have a 20 month old here who is only just starting to put weight on, he was embarrassingly skinny until now.

Dogs have thyroid gland problems, just as people do. Too low, too high, both happen and produce just about opposite signs in affected dogs.

Overweight, inactive, poor hair and skin condition, are commonly seen when the thyroid doesn't produce enough hormone. The opposite, or too much thyroid hormone, commonly results in an active dog that has lost weight, in spite of eating 'well', and seems healthy otherwise. Take him to the vet, with a sample of his BM for a worm test, and explain your concerns to the vet. There is nothing to gain in trying all sorts of different diets to get weight on him until you determine there isn't a medical problem.

He is one of those long hot dogs a dauchin I think that's how you spell it he ia 1 1/2 years old. He eats like a hog they give him buddy boy dog food.The other dogs they have are nice and fat.Think I will take him to the vet as advised for a worm test thank you very very much.

Thank you for the response. Be sure and tell the vet he is an 'eager eater', OK? Best wishes to you both.