It is nearly impossible, you just have to wait and see who lays the eggs
-Some people do have methods, but they dont always work
-Here is one method (only for baby pigeons)
At the age of banding, place your right hand over the top of the bird
with your thumb aiming at the head of the youngster.
Then turn it up side down so the vent is facing you.
If the vent is a smiley face it is a cockbird, a frown is a hen.