Yes, they generally stick them onto the bottom of plant leaves, and the prefer broad leafed plants. They should be relatively easy to see if you are looking in the right place, especially since a mass of them will likely be there.
Rasboras are not one of the easier fish to breed. So, there could be any number of reasons why they are not spawning. Also, it is possible that they are spawning and all the eggs just get eaten.
It helps to keep the water nice and clean, and condition the fish with live foods. Eggs need aeration, so a jug might not be the best idea. You can do a bucket with an air stone though or something similar if you do not have access to another tank. They would probably be ok with molly fry if the fry were small enough. IME, mollies are pretty voracious eaters, so you would have to keep an eye on how big the mollies are to make sure they don't swallow harly fry.
Keep in mind, harlies are known to be a bit finicky about spawning, so don't hold your breath and don't take it personally if you cannot get them to spawn. If you are really serious about wanting to breed them, you would be best off with a couple of grow-out tanks solely for these fish. If you just have fish in your tank that look like they could spawn and you are curious, then just do your best with what you have and let it ride.
That is about the best advice I have for right now. If somebody else with experience with this particular species spawning reads this, I am sure they will chime in with more complete info.