Nazahn, Revered Bladesmith

When Nazahn enters, search your library for an Equipment card and reveal it. If you reveal a card named Hammer of Nazahn this way, put it onto the battlefield. Otherwise, put that card into your hand. Then shuffle.
Whenever an equipped creature you control attacks, you may tap target creature defending player controls.

Commander 2017

When Nazahn, Revered Bladesmith enters the battlefield, search your library for an Equipment card and reveal it. If you reveal a card named Hammer of Nazahn this way, put it onto the battlefield. Otherwise, put that card into your hand. Then shuffle your library.
Whenever an equipped creature you control attacks, you may tap target creature defending player controls.

Treasure Chest

If a creature is attacking a planeswalker, its controller is that creature's defending player.

If more than one equipped creature you control attacks, Nazahn's last ability triggers once for each of those creatures. It doesn't trigger additional times for additional Equipment attached to an attacking creature.

Nazahn's last ability can target a creature controlled only by the defending player who is being attacked by the attacking creature that caused the ability to trigger. For example, if an unequipped Nazahn is attacking player A and an equipped creature is attacking player B, Nazahn's ability can target only a creature player B controls.