This question may be so elementary, I am almost embarrassed to ask it. But I must.
Is there a "right or wrong" direction which a train should run on a layout? (Clockwise vs. counterclockwise)
I believe I have seen them running both ways.
Which ever direction you want
Since a loop on a model railroad is a concession made by modelers to fit a layout into available space, there is no "wrong" direction to run the train. Since the prototype railroads (yeah, I know, there will be exceptions) tend to run point-to-point, there really isn't a "right" direction to run it, either. Install double-track mainlines and you can run both directions!
On most US railroads with a 2 track line the train closest to you should run counterclockwise.
Not all do so check that the railroad you model does.