Knowing who laid what was a huge obsession for me in the beginning. I guess I was a stalker around the coop for a while. But I just had to know. Now that I know what each girl’s egg looks like I don’t obsess over it. Like it was said earlier, you kind of have to be in the right place at the right time. But you can make a point to hang around the coop on one of your days off and just scope out what Chicken goes in, which nest they use and then what egg is deposited.
Every egg is different in some way, colored ones anyway. Shiny, matte, smooth, splotchy, bumpy, long, short, round, oval, etc. Some hens will leave more bloom (coating) on the egg and some will scratch the crap out of their eggs. I have three girls that scratch the eggs so bad, mostly with their beaks, that I can’t sell those particular ones. Well, I could as there is nothing wrong with the egg, but they just feel so rough, so I don’t.
I also keep a daily count of what eggs have been laid. I mark each day on my BYC calendar and then transfer the data to my excel spreadsheet. I just track the number of each Brown/Blue/White/Green. So my calendar has this weird gibberish on each day like 14/6/1/5. Yep, I’ve only got one line white egg layer.

I’ve done this for almost four years now.