Which of the following diagnostic procedures is most commonly used to confirm the diagnosis of psoriasis?

Mr. Santos, a 45-year-old male, presents to the clinic with red, scaly patches on his elbows, knees and scalp. He complains of itching and discomfort. Upon assessment, you notice well-defined, raised, erythematous plaques with silvery scales. The patient reports that the symptoms have been present for several months and have worsened recently.