For most species of Cory your going to find that when adult males and females are compared from a top down angle the males will be more slender or narrower than the females. Especially looking down at the belly area below the dorsal fin. The female even without eggs are "fat" looking compared to males.
During breeding the males will chase after the female in a very sociable manner, and to prompt them to breed just gradually raise the temp of the tank to around 83 over a week or so then drop the temp over night to around 78-79. This simulates the natrual tendencies of their native habitat to have rains fall and cool the water very quickly. Feed live tubifex to the parents for the best health and they (If both sexes present) will breed about once a week to 10 days.
I suggest this or other corydoras books:
"Catfishes" by C.W.Emmens and Herbert Axelrod and "A complete introduction to corydoras and related catfishes" by Dr. Warren E. Burgess.
If you can't find either of these cheap books just go to the local library and look at them for a better understanding of the top down apperances of cory's.