"You have to move the sketch out of the body."
I figured out how to do that - I need to detach it from the face, so there are no solids to select when creating the job (with the sketch selected), just the sketch. After detaching the sketch it still appears to be part of the body, however. Thanks!
However, when I go to create the engrave operation, I can only add 1 line to the base geometry. The gcode shows that only the single line is carved. Is that a known bug?