According to AMEDDC&S PAM 350-10 , the written test covers only medically related subjects:
The following references are used to derive the written test questions:
(1) FM 8-10-6, Medical Evacuation in a Theater of Operations Tactics, Techniques, and Procedures.
(2) FM 21-10, Field Hygiene and Sanitation.
(3) STP 8-91W15-SM-TG, Soldier’s Manual and Trainer's Guide, MOS 91W, Health Care Specialist, Skill Levels 1/2/3/4/5 (skill level 1 tasks ONLY).
Know the capacity of every type of vehicle and aircraft for ambulatory and litter patients.
Know how to treat hot and cold weather injuries.
Know obscure injuries (like white phosphorous wounds).
Know what situations are best suited for each manual carry (i.e., what is the best manual carry to use if you are in a tactical environment and your casualty has a broken leg?).
Be up to standard on all field sanitation subjects. (Given a unit size in personnel, how many straddle-trench latrines do you need?)
All the references should be studied, at least briefly. DO NOT wait until you are in the field currently doing the lane testing to start studying for the written test. The answers are not going to be different out there. Be prepared for the written test long before you go to the field.
These questions can get obscure. For instance, what happens to the field medical card AFTER the casualty is evacuated all the way to CONUS? AR 40-66 will give you the answer.