What type of epithelium are the pancreatic Islets of Langerhans?
I think the image you've attached lacks clarity. If you see the image below, you could say that the epithelium is cuboidal with central rounded nucleus.

Unlike the oval nuclei of columnar epithelium, rounded nucleus suggests that they are cuboidal in shape.
The image is from https://webpath.med.utah.edu/HISTHTML/NORMAL/NORM010.html