well, to figure out where they'll lay eggs you gotta think like a gecko mom. she's gonna want to lay the eggs in a spot that stays cool and moist, but not wet. it's kinda hard to tell you EXACTLY where she'll lay them, but you can pretty much narrow it down. now i havent gotten sikorae eggs yet, but i have gotten eggs from phantasticus, pietschmanni, and henkeli. unfortunately the pietschmanni did the best job of hiding their eggs, and i didnt find them until after they had gone bad. only once have i had an egg buried, and it was only one of the two eggs from the clutch. they were from my satanics, the 2nd clutch i ever got. still dont know why the one was buried and the other was on top, possibly because when i first started keeping phants i gave them very little ground cover. other places i've found eggs from phants are in a bromeliad, under a dead leaf, under a fairly thick bunch of pothos, at the base of a plant sitting right next to a fake stump made of corkbark. the single clutch ive gotten from my henkeli was at the base of a few thick branches, under a little bit of moss fiber (not totally concealed, but pretty well hidden in the moss). and with my pietschmanni, i found both a fertile and an infertile clutch at the base of another corkbark stump, with some more moss fiber that concealed the eggs so well that i found them too late.
so i wouldnt necessarily count on the eggs being buried, but i cant guarantee you they wont. if you could snap a pic of your enclosure, i might be able to point out some spots that look like they're worth checking. something that might be worth trying out is adding a flat piece of bark around the bottom of the cage with a pocket beneath it, perhaps with some moss fiber. if you make it look particularly enticing, it might just work out, although i havent actually tried it myself.
what i find out works best is staying in fine tune with your geckos, and observe the female's nightly behavior if you think she might be gravid. unless she simply doesnt have enough to climb around on, you'll barely ever notice her on the floor of the enclosure (unless she's diving for crickets). every time i look in an enclosure, i make sure that everyone is accounted for, and i do it at least once daily. this helps you learn their daily hiding spots (almost all of mine tend to pick out a sleep spot and stick with it) or even notice if anyone is missing. my satanics will walk the bottom of the cage around the time they're getting ready to lay (sometimes they start searching the bottom for a good spot to lay a day or two ahead of time.
so theres really no definite place for a female to lay, but she'l most likely pick out the best spot. it's likely to be a spot with good cover, perhaps under a plant, perhaps in a small crevice you didnt even realize was there. just know your animals well, along with the possibilities in their enclosure.