It's hard for any dealer's to find service writer's that know anything about fixing or maintaining a vehicle because most knowledgable people would rather turn wrenches than deal with customers. A good tech also makes more money than a good writer.
As far a training, most writers do receive training from the manufacturer, but it is geared more toward selling service. They do not receive any technical training. Writer's are told by the manufacturer to follow their guidlines to the letter. They are trained by the dealership to sell as much as they can.
Not many customers ask technical questions, and do put their full faith in the service department to take care of their vehicle. Writers,for the most part do not have answer even basic technical questions, but when they do, they are expected to answer truthfully, even if the answer is "I don't know, let me go ask one of the techs."
Also keep in mind, the writer is your point of contact, and the person you are going to hold accountable, and they know that very well. They also know that their dealership may have practices that don't follow the manufacturer's recommendations, like, using 5w30 conventional oil instead of 0w20 synthetic.
When you question them on such items, they are not going to want to accept blame for that, and then have to tell you that they can redo the oil change, but you will have to pay the difference in cost for the 0w20 that they will get from the parts store at full retail and then mark up 100%.
There are good writers out there, and they are knowledge junkies. They will ask questions of their techs and read everything they get their hands on. They are the ones that love cars, but also enjoy working with people. If you are a technically inclined customer, sure, you will stump a writer. It's not their job to fix them, it's their job to be able to communicate your concern to the technician in detail, and then relay what happened to repair your vehicle in simple layman's terms. But again, the best writers will go above and beyond to learn about the vehicle that come into their shop.