I have done part time, floated to, endoscopy for years. I have never used a resource book. I do love to learn and study so I understand your question.
I don't know....once in a while I would try to get some journals but never found one that offered much. Then I just got lazy, ha ha.
I don't know how familiar you are with endoscopy? I don't know what your job will entail?
ONLY moderate sedation?????
ONLY assisting the doctor, tech, and anesthesiologists???
Actually working as the "tech"? Working along side the gastroenterologist, passing the snares, dilators, etc.?
You tube is a good resource for what goes on in an endoscopy unit.
It may be best to get through orientation, work a while, ask a lot of questions...when you are new it is a great time to ask away...tell the doctors, techs, anyone you work with..."I'm new, do you mind if I ask about such and such." Then as you find out what your duties are you will be you can find resources more pertinent to what you are doing or maybe get some good ideas from co-workers about books, journals, etc.