
If you have his papers and he is kennel club registed, you are listed as the owner, then yes you can. Got friends who got a rescue dog, who had 1 cc, dog now has 4/5cc's!
However if you don't have his papers or registerd owner you can still show but only at companion dog shows, which are rare this time of year, they are summer shows, only for fun, and are a lovely afternoon out!