Is Nagilum (from the episode Where Silence has Lease) omnipotent and omnipresent? He's not omniscient as he is doing an experiment to learn more about humans.
He seems omnipotent as he can conjure up any reality (though it is not clear if this requires the expense of limited resources). He seems omnipresent, or at least have the ability to transport anywhere. Even when the Enterprise was out of the void Nagilum communicated to Picard on a computer.
EDIT: after reading Stefan's answer I wondered, can one be omnipotent without being omniscient? If someone was omnipotent wouldn't they be able to use there "powers to do anything" to make the experiment to satisfy their quest for knowledge? If they had a limited capacity to learn or recall knowledge couldn't they use their power to do anything to remove this barrier?