How do we determine whether the airfoil trailing edge should be cusped or pointed? I'm working on a project and I need to decide whether an airfoil has a cusped or pointed trailing edge given the x and y coordinates of the airfoil.

What is the difference between the two trailing edges?
Both cusped and conventional airfoils have pointed trailing edges. The lower trailing surface is concave on cusped airfoils, so plot it and get your straightedge.