I know to keep a continuous supply of water in the tray at the bottom of the plant, but do I also need to water the plant on top directly? If so, how often? If not, how does it draw water from the tray?
There should be no need to water from the top as long as you keep some water in the tray.
Water is very cohesive. It kinda sticks together. The water is pulled up through the soil through capillary action. As water moves up to fill the tiny airspaces in the soil it also pulls more water up with it. This continues all the way to the top.
Kinda like if you take a paper towel, turn it on its edge and dip the very edge into water. Try it and it will help you to get a picture of what is going on.
Hope this helps,
Let me preface this by proclaiming my ignorance and lack of experience.
That said, and reiterated,
I have read that occasional watering from the top, or flooding of the pot by using an oversize saucer and filling it up, can help the plants by oxygenating the soil and preventing anaerobic bacteria and mold from taking hold.
I've solved this and other problems for myself by putting the little monsters outside for the summer, where they seem to like it best.
Rainwater in Columbus has a low PH (my litmus reads PH 5) and is full of oxygen. We'll see if the pollutants are too much for them.
I water mine from the top periodically as well as keeping them in saucers of water. When I see the water level drop in the saucer, I give them water like any other plant. And of course, being outside, they get rained on which is nature's "watering from the top". Every now and then they get a gentle misting to remove stubborn fly husks and dirt from the rain splashes.
Occasional topwatering or leaving the pots in the rain are both very good ideas as they will oxygenate the substrate and will leach out any accumulated salts and products of decomposition. Rainwater that falls is "alive" having picked up some Magic in it's falling. I shake the watering bottle to dissolve some O2 in it before watering from the top.