Medical school. General practicioners have gone to medical school and most have had an internship and residency in family medicine. Many have tremendous training in the er, icu, and in practice. The gp as your call them (family physician) does not hold themselve out as "the expert" in head trauma but are usually very knowlegeable. They are the ones out on the football field making sure your children are safe!
Head trauma. Usually gp's are family practice doctors now and depending on their training and er experience, they may know a lot. Ask them directly. If you are looking for an expert on head trauma, see a neurologist and a neuro surgeon.