one usually, maybe two.
but it would more likely be one dubia plus one cricket, or one dubia and a silkworm, or one dubia plus a terrestrial isopod, or a dubia and a butterworm.
3, but males are only 3x heavier than an adult cricket. Females are 6x heavier, so thats a dozen crickets in just 2 feeders with 2x the protein of crickets.
At least one adult dubia, and maybe another smaller one as well. As sandrachameleon said, it's more often one dubia and some worms or crickets as well.