Student or Learner
What other expressions do you have for these?
He cannot make a living = He cannot earn his keep = He is not worth his salt.
A :He is the most hard working person in this office
B : Yeah, he's really worth his salt.
I can't think of any that directly involve an estimation of someone like that. But we do say of good workers that they "carry the load" or "pull their weight." You could even say they are someone you want "in your foxhole."