Final answer:
The keratinocytes with spine-like projections are found in the stratum spinosum, a layer of the epidermis named for its spiny appearance after staining, though this feature is not evident in unstained samples.
Step-by-step explanation:
The keratinocytes with spine-like projections which give rise to the name of their cell layer are found in the stratum spinosum. This layer is characterized by keratinocytes that interlock through desmosomes, creating a spiny appearance after staining, which is not visible in unstained samples. The stratum spinosum is part of the skin's epidermis and plays a role in the skin's barrier function and immune response, with keratinocytes in this layer beginning to produce keratin and containing interspersed Langerhans cells, which act as macrophages.