I haven't used Daz3D character specifically. What I recommend to do in general is to add the eye prefabs to your scene and then them a child object of the "eye" bones in your character. Then set the position of the eye prefabs to 0,0,0 and the rotation to 0,0,0. This should automatically put them at the same position and rotation as the eye bones... then you can just tweak a bit as a necessary from there.
Once you're done with one character, you should be able to duplicate and copy to your other daz characters without much trouble (assuming they use the same or similar scale and setup).