Final answer:
The Stratum basale is the epidermal layer with cells undergoing division to form new keratinocytes.
Step-by-step explanation:
The layer of the epidermis that contains cells undergoing division is the Stratum basale. The Stratum basale is the innermost layer of the epidermis and hosts the stem cells responsible for producing new keratinocytes through cell division. These new cells are then pushed up through the different layers of the epidermis as they mature, eventually reaching the surface and forming part of the Stratum corneum, the outermost layer composed of flat, dead keratinocytes.