Dermatiologists (skin doctors) are interested in looking at skin anywhere on your body which may be abnormal. Moles, discolorations, lumps in the skin (epidermis) can sometimes lead to Cancer and that they want to prevent.
It is not unreasonable to ask a Dermatologist to examine your entire body, "privates" perineum, breasts, face, ears, toes or anything else you wish. No specifics are required of you to have this done. YOU are paying the doctor and he OR SHE--(your choice, regardless of your gender) has an obligation to examine you according to any general, (or specific,) reasonable request. All of us have some features on our skin we can mention, but it is entirely OK to ask for a full body exam and leave it at that. If you are asked about any areas of special concern, you can answer "nothing specific" or list anything you may want special attention to.
You can study the conditions which cause dark spots and other skin difficulties by searching for "Human Skin Cancer" or Skin conditions - Dermatology" on line. You may learn of some extreme examples, but know they are rare.
Dermatologists are specialists, and generally do not deal with problems UNDER the skin unless the skin itself is affected. Dentists can often deal with tissue or "skin" conditions inside the mouth.
Very many Dermatologists have another person in the room while doing the exam. Usually this is a female assistant, probably not a nurse (to keep the doctor's payroll costs down>😉 This person will perhaps take notes as the doctor cites some location and condition seen.
And this assistant will frequently of not always need to be watching the exam in case some patient should allege inappropriate action by the doctor. Occasionally, a mirror in the room will be angled so this person can see you, but you (maybe because of where the doctor is standing) cannot see that person.
The common treatment for skin areas which MIGHT become Cancerous is a nitrogen, or "freeze gun" which can be a bit painful briefly.
If you want to avoid skin problems, minimize your exposure to the sun. A tan may be beautiful now and yet long exposure over the years--most commonly to the face, arms and hands--can mean many trips to the Dermatologist, and increased risk of Cancer.