How many points does the perspective in the viewport use and is it changeable? I know blender can display both orthographic and perspective projection. But, when we look at a cube in blender's viewport, I'm unable to distinguish by eye, if the projection in the viewport is a one-point, a two-point or a three-point perspective. What does blender use, and is this something changeable?
I'm no architect, but this should only depend on your camera alignment.

1 point perspective - camera aligned to 2 axis
2 point perspective - camera aligned to 1 axis
3 point perspective - camera not aligned to any axis

As given in the link in the comment and mentioned by  @haarigertroll mathematically these are special  cases of the one point perspective.