Learn Polish: Czy wiesz, kiedy jest rekrutacja? - Do you know when the recruitment is?

No, Polish keeps it simple here! In English, a direct question ('When is the recruitment?') changes order when it becomes an indirect question ('...when the recruitment is'). In Polish, the word order stays exactly the same as the direct question: Kiedy jest rekrutacja?

Why is there a comma before kiedy?

Polish punctuation rules are very strict about separating clauses (parts of a sentence that have their own verb). You must always put a comma right before the word that connects the two parts, which in this case is the question word kiedy.

Could I use znasz instead of wiesz in this sentence?

No, you must use wiedzieć (here in the 'you' form: wiesz). Use wiedzieć for knowing facts or information, especially before question words like kiedy, co, or gdzie. The other verb for 'to know', znać, is only used for being familiar with a person, place, or noun.

Since the sentence has the question word kiedy, why do we also need Czy at the beginning?

These two words are doing separate jobs. Czy turns the first part of the sentence into a yes/no question (Czy wiesz...? = Do you know...?). Kiedy simply connects the second part of the sentence and acts as the word 'when'.