Can you give a little more context because it is possible that you need to use another verb. It is also possible that both of your phrases could work. It depends on the context of the entire text. Are you talking about a person who attracts attention or a person who requires attention?
Person who attracts attention, for example, a model, an actor, a very charismatic, confident person: "The person who commands attention is the one who ..."
Person who requires attention, for example, a customer, a patient, etc.: "The person who demands attention is the one who ..."
You would use "The person demanding attention is the one..." in the following context:
Person A: Which customer needs to get a refund right away?
Person B: The customer demanding attention is the person standing over there.