How do I cook store-bought glutinous rice dumplings?
I would not follow the advice of boiling them for three hours, you will likely have nothing left! I would not boil them at all in fact, most dumplings you get from asian supermarkets in western countries are made so that they can be steamed from frozen for 15-30 minutes and then eaten. They are often produced for the catering trade, you see, so quick cooking times are important. The picture you posted looks like they are possibly fried, but it's hard to tell.  

I am making the assumption you are not in Asia, and this is a specialist supermarket, so I would simply call up the supermarket and ask. It's pretty likely someone there will be able to speak with you. 

If not, the important thing is to make sure that the dumplings are cooked throughout to at least 160F (72C), this will at least make them safe. I'd recommend using a digital instant-read thermometer for the job. The three methods I know of to cook pre-made dumplings are:


Steam: you can use a bamboo steamer if you have one, but any steamer will do really. If you can get banana leaves use them to line the bottom, but if not use something to line the bottom of your steamer because these things stick like glue!
Fry then steam: this is done with a wok, you brown the dumplings in the wok in some oil, then you pour a bit of water in and cover. The dumplings then steam under the cover, and the oil gets vaporized as well giving the dumplings a nice sheen. I've only used this for small wonton-style dumplings, I wouldn't recommend this method for your big ones although there's no reason you couldn't try it. Just remember that pouring water into hot oil causes spurts, a top tip from me to avoid being singed would be to hold the cover over and pour the water in through a small gap. Keeps the mess down as well
Deep frying: I'm sure shallow frying would work as well, however you must thaw these out before frying them. Throwing frozen dumplings straight into a pool of boiling oil is dangerous! I don't have a deep fryer and I don't like the mess of shallow frying so I avoid dumplings that require this. Also, not many dumplings are deep fried


All in all I'd try steaming one of them for 25-30 minutes and then testing it. Vary the steaming time accordingly.