(Book 13.9 III. Read 13.1 for a refresher on circulation, vorticity, and Stokes' theorem.)
Streamlines are lines that are everywhere in the direction of the velocity. Vorticity lines are lines that are everywhere in the direction of the vorticity.
Nope, vortex lines do not have to end on the boundary or be a closed curve.
You should now be able to make 13.8