Moisture in he attic can only come from 2 places. 1/ through the roof, as in a leaky roof or because of ice damming. or 2/ from the living space, warm humid air enters your attic, comes in contact with a cold surface & condenses. In view of your comments, this seems to the your problem.
This is not am insulation or ventilation problem, so trying to solve it with insulation or ventilation will not work, in fact, it could make the problem worse. What nees to be done is find where the in-house air is leaking into the attic & stop it. You may need to contact, not just an insulation contractor, but one who specializes in solving such problems. A good source to find such a contractor is your local Utility company.