Not sure if you can tell by looking at them if they are carrying eggs. Even so, as Mike noted above, breeding in captivity is not that easy. Fish often lay eggs that do not get fertilized, get eaten, or otherwise don't survive to hatch. And some have very specific breeding habits/needs. For example, synondontis multipunctatus trick mouthbrooding cichlids into caring for their babies (they are know as "cuckoo catfish" for this reason). I don't know about your particular type of synodontis, except that google suggests they do not tend to breed in captivity.