Really depends on what it is for! if you want to do it with events and not behaviors, and the origin is in the center, you can do:
Spawn BoxObj
Set position to X: (Self.Width/2), Y: (Self.Height/2)
Spawn BoxObj
Set position to X: WindowWidth-(Self.Width/2), Y: (Self.Height/2)
Spawn BoxObj
Set position to X: (Self.Width/2), Y: WindowHeight-(Self.Height/2)
Spawn BoxObj
Set position to X: WindowWidth-(Self.Width/2), Y: WindowHeight-(Self.Height/2)