Learn Italian: Chi sarà il nuovo capo a gennaio? - Who will be the new boss in January?

sarà is the third-person singular (he/she/it) future tense of essere (to be), meaning 'will be'. We use this form because the question word Chi (Who) is treated as a singular subject, just like in English.

Why does sarà have an accent mark?

The accent mark tells you to stress the final vowel (pronounced sah-RAH). In the future tense, all 'I' forms end in an accented -ò and all 'he/she/it' forms end in an accented -à.

Why is the preposition a used for 'in January'?

When talking about months, Italian uses either the preposition a or in. Both a gennaio and in gennaio mean 'in January' and are totally correct. Also, notice that months are not capitalized in Italian!

Could I say il capo nuovo instead of il nuovo capo?

Yes, both are correct. However, nuovo is one of the few adjectives that very commonly comes before the noun. Putting it before the noun is the standard way to say 'the new boss', while putting it after places extra emphasis on the fact that the person is brand new.