Looked at a house that had an electrical, split system with the evaporator in the attic. The emergency drain was visible in the front gable, but I did not locate the primary drain.
There was not a primary drain on the exterior wall, and no drains tapped into the sink / basin drains.
Can the evaporator be drained into piping in the attic?
Needs a P-trap?
Nope can not connect to attic vent even with P-trap unless it is a high efficiency furnace and you stated it was electric so that ends that.
Should be able to follow the drains from the A-coil even if they are buried in insulation. My guess is the primary drain is connected somewhere to a plumbing vent and is not allowed.