Learn Italian: Nessun osservatore è pronto per questo talento.

The adjective pronto (ready) requires the preposition per when introducing what someone is ready for. This applies whether it is followed by a noun, like questo talento in this sentence, or an infinitive verb.

Why is it nessun osservatore and not nessuno osservatore?

The adjective nessuno (no/not any) drops its final vowel following the exact same rules as the indefinite article uno. Because you would say un osservatore (since the noun starts with a vowel), you must use the truncated form nessun osservatore.

Why isn't there a non before the verb to make it a double negative?

In Italian, when a negative word like nessun comes before the verb as the subject of the sentence, you do not use non. You only use the double negative structure if the negative word comes after the verb (for example, non è pronto nessun osservatore).

I thought osservatore meant observer. Why is it translated as scout?

While its literal meaning is observer, osservatore is the standard Italian term used in sports and entertainment for a talent scout. You will sometimes see the English loanword scout used in Italian as well, but osservatore is very common and natural here.