You determine whether you draw a card or put a +1/+1 counter only as Primal Empathy's triggered ability begins resolving. Players may respond to the ability to try to change which happens.

If the greatest power among creatures on the battlefield is shared by a creature you control and a creature you don't control, you draw a card.

If you don't control a creature with the greatest power, you choose which creature gets a +1/+1 counter while the ability is resolving. Players can't take actions in between the time you make this choice and the time that creature has a +1/+1 counter.

If you control no creatures, you do nothing as Primal Empathy's ability resolves. If there are no creatures on the battlefield at all, you don't draw a card.