The main reason that folks get fecals done is to check for internal parasites. A vet can see other things as well, but usually to check others things they use blood tests or other methods for evaluation. When any test is done, the vet will tell you of the results and if anything out of the ordinary is occuring, and a good vet will discuss even what the normal readings of a test mean.
You do not need to ask the vet to look for anything, but merely state your concerns. Usually you will be "interviewed", for lack of a better word, to find out the problems and living situations of your animal before seeing the vet. This way the vet can determine what is going on and what to be more concerned about in that respect.