I don’t believe in omnipotent or omniscient gods, only normal ones, but I’ll bite your hypothetical.

An omniscient god would necessarily have a perfect sense of empathy. They would know what everyone is feeling. And to know a feeling is to feel it, so they would feel every feeling in the world, at full intensity. Obviously such a being would need to be all emotionally resilient as well as all knowing. But they would care for the problems of mortals, because they would feel what mortals do. Perhaps in such a hypothetical, prayers are simply a person attaching a feeling of urgency to their needs, in hope that their god will feel this urgency too and respond.

But of course, I believe in normal gods, so this is all just an intellectual exercise to me.