Hi,
As many as they want in 10-15 minute period. I usually give about 5 insects (dubias, crickets, etc) at a time and keep feeding til they don't want anymore. If feeding crickets please cannot stress enough, find a way to get them out of the enclosure they will bite and feast on your beardie and that is no good. There is no exact amount per feeding just make sure they can eat as many in that time frame. What also might be handy is to have a separate enclosure you can put the feeders in, just make sure its big enough for your beardie to fit inside of and able to eat.