Which term refers to the ability to do work?

A term that refers to the ability to work is "si puedo trabajar" or "tengo la abilidad de trabajar" or if you want to be as precise as possible then you could put "Yo tengo la capacidad para ser trabajo"

Explanation:

For a:"si puedo trabajar." that means "I can work."

For b: "Yo tengo la Capacidad de trabajar." that means "I have the ability to work."

For c: "Yo tengo la capacidad para ser trabajo." this means "I have the ability to do work."

personal note: i would prefer to use c but after all it depends on the situation or wheather you talking to some one older than you or in a higher postion than you.