Learn Polish: Oprócz szefostwa nikt nic nie wiedział. - Apart from the bosses, nobody knew anything.

The suffix -stwo is used here to create a collective noun. While szefowie refers to multiple individual bosses, szefostwo refers to "the bosses" as a unified group, similar to "the management" or "the leadership".

Why is the word written as szefostwa instead of szefostwo?

The preposition oprócz (apart from / besides) always requires the noun that follows it to take the Genitive case. Because szefostwo is a neuter noun, its Genitive form takes the -a ending.

Does the masculine verb wiedział agree with szefostwa?

No, the verb agrees with the subject nikt (nobody). In Polish, the pronoun nikt is grammatically masculine singular. It always requires the masculine 3rd person singular verb form in the past tense (wiedział), regardless of the actual gender of the people involved.

We have nikt, nic, and nie right next to each other. Is this a triple negative?