Is there a spell that it will gain gold per second?

[FUJI]

Is there an passive ability that it will give you an amount of gold per second?

 

[Karzama]

No but you can easily trigger it. Just periodically set a unit group as units that are alive with that passive and give gold to the owning player, if you have levels just check the level of the ability and give gold accordingly.

 

[Wietlol]

Answer: Nope.

But as Karzama said, you can easily trigger it.
Create one group that contains the units that have that spell.
Check if the unit is alive and if the unit has that ability.
If not, remove them from the group.
If true, give gold to player.

Pick every unit in entire map at initialization and check if they have the ability and add those in the group.
Make a trigger that will catch every unit that enters the entire map and check if that unit has the ability.