Which healthcare professional is typically a secondary care provider?
nurse practitioner
physician
dermatologist
physician’s assistant

Here is what I know:

Physician is a primary care provider.
Nurse practitioner & physician assistants can serve as primary care providers under the direction of a physician. Because they can diagnose & treat certain diseases as well as write prescriptions for certain medications to treat said diseases.

Dermatologists treat diseases of the skin. To see one may require a call from the physician known as a referral. A patient may also just walk in to be seen by the dermatologist. But the dermatologist cannot treat heart, muscle, diabetes, sprains, etc.
so I would say the dermatologist is a secondary care provider.