Yes, your employer can require you to do this: your employer can require you to do anything not intrinsically illeag, and there is nothing illegal about a hotel employee watching an incompetent guest. As to liability: you could be held liabke for your own negligent (careless) or otherwise wrongful action, such as if while watching him, you walk away and he is injured while you are inattentive. You would not be liable for anything not your fault, such as if he had a seizure or did anything to injure himself while you were watching him responsibly.