Learn Italian: L'impiegato deve rifare tutto il lavoro. - The employee must redo all the work.

The prefix ri- acts just like the English prefix "re-", indicating that an action is being repeated (the iterative prefix). Since fare means "to do" or "to make", adding the prefix creates rifare, meaning "to redo" or "to do again".

Why do we need the article il in tutto il lavoro?

In Italian, when tutto (all) modifies a noun to mean "all of the" or "the whole", it must be followed by the definite article. While in English you might sometimes just say "all work", Italian strictly requires the article here: tutto il lavoro.

Can l'impiegato be used for any kind of employee or worker?

Not exactly. While it translates to "employee", impiegato specifically refers to a white-collar office worker or clerk. If you were talking about a blue-collar or factory worker, you would use operaio, and a general term for a worker is lavoratore.

Why is rifare left in the infinitive form rather than being conjugated?

It directly follows deve, which is a conjugated modal verb (dovere - must/to have to). Whenever you use a modal verb, the verb that immediately follows it must remain in its infinitive (dictionary) form, just like how we say "must redo" instead of "must redoes" in English.