If a spell deals damage to one or more units at Void Gate and one or more units somewhere else, which parts of that deal Bonus Damage?

The Bonus Damage from Void Gate is only for damage being dealt to units at Void Gate. It will receive errata to clarify this. (As a bonus, Bonus Damage will now be fully defined in the rules.) Spells and abilities deal 1 Bonus Damage to units here. (Each instance of damage the spell deals to a unit here is increased by 1.)

Related: Rule 713, Rule 715.2, Void Gate