I get a little lump on the edge of my circumcision scar. I can pop them an a little black thing comes out. I get about one a year. What is this?

Comedones. What you describe are likely common skin lesions known as comedones. While tempting, "popping" them can lead to infection under the skin in the area of the hair follicle where the sebaceous glands ( where the cheese-like sebum is produced) are located. When exposed to air the tip of the sebum core turns black. Hence, the nickname "blackheads".