Onychomycosis is a fungal infection of the nails. Alters the aesthetics of the affected nails and does not usually cause discomfort
A dermatologist is a doctor who specializes in diseases of the skin, hair, nails and mucous membranes.
A podiatrist is a professional in the diagnosis and treatment of diseases and disorders of the foot.
A doctor or family doctor is responsible for diagnosing and prescribing medical treatments to patients. The family doctor refers to patients where a specialist when a specific treatment is required.
Remember that for the proper selection of health professional that treats onychomycosis you must consider the nature, severity and symptoms you are presenting.