I'm sure that there are some "with the knack" that have their paper, but remember that "the knack" isn't offered in college.  No classes.... no credits... no manuals. nada.

Too many high paid people are "Knackless".
I agree with Volvo Farmer.  
Years ago I was under a machine when a newly hired Eng. asked to borrow "a wrench" she wasn't sure what size she needed....  I handed her a 7/16 (it's what I had in my hand) she returned a few moments later and said "it's too small, do you have a 8/16?".

That, and no "creativity".  it's one thing to take it apart.. and put it back together, but to see it's faults and improve it.

My vote goes to the "jack of all trades".   I understand that he's the master of none, but many of the "masters" of one are "at best" just ONE.  

I've seen the duct tape and wire tie theory at work.  A machine "breaks down" the Eng.says a new part will take a week, the low paid maintenance man fixes it with a door spring and a wooden dowel.  Took us 8 minutes.