After he found out the boss was stealing money from the company, Jeff was taken off the production line and given a sinecure as “safety monitor,” a job at which he did little or nothing.
The word that best completes the sentence is sinecure.
A sinecure is a job or position that requires little or no work and provides a comfortable income. In this context, Jeff was given the role of a "safety monitor" as a pretense to keep him away from the production line, but in reality, he was not assigned any meaningful tasks.
Therefore, the correct answer is sinecure.