I look at JoT as being a renaissance man, sort of like Thomas Jefferson, Leonardo Da Vinci, MacGyver, or the Most Interesting Man In The World.
So not just 'stuff the character learned on the job', I say, ALL skills at 0.
But the JoT + is subsumed in an education roll- I allow a chance for knowledge to lower the difficulty of a task, so say an INT 5 EDU A character could be quite resourceful even if not the brightest thinker.
Of all the suggestions I read here, I like the JoT level equals number of times to use one the best.