Do you mean do a poop?
If your dog eats a meal once a day, he/she should poop once a day....fed twice, should poop twice a day....etc. Though this can vary, as many dogs can squeeze out 3!
What is important is to find out if there is anything going on which could be causing a blockage of some kind. For instance, did this suddenly start happening? Did your dog get constipated after eating a rawhide chew, or a bone? Or playing with a toy? Or does he/she chew on anything else, like clothing, furniture, pieces of cardboard....etc?
If the answer is yes, or you think this might be the case, then contact the vet ASAP, and take your dog in to be checked.
If not, then does your dog get enough fibre in his diet? Get a good quality dog food, and check there is sufficient fibre in it. Also you could add some plain steamed or lightly boiled carrots to his food, or even a few peas, or beans. Some vegetables are not good for dogs, and some are very good. I think the best thing would be either to ask your vet about this or do a search online to find out which foods are toxic or bad for dogs, so you would know which ones are safe.
Another important thing is water. Does he get enough water?
And exercise is important too. Most dogs need a good walk and also a good run off-leash (or vigorous play of some kind) I always find that my dog will do her business after a good run, followed by a steady sustained walk for a while.