Learn Italian: Di chi è l'orecchino? Lo deve descrivere. - Whose earring is it? You must describe it.

In Italian, there isn't a single exact equivalent for the question word "whose". Instead, you literally ask "of whom" (di chi). Notice that unlike English, where you can say "whose earring", Italian separates di chi and the noun (l'orecchino) with the verb (è).

Why does the translation say "You must" when deve is the he/she form of dovere?

The sentence is using the formal "you" (Lei). When speaking to someone formally in Italian, you use the third-person singular conjugation. If this were informal, it would be Lo devi descrivere.

What does the lo in lo deve descrivere do?

Lo is a direct object pronoun meaning "it". It refers back to the masculine singular noun l'orecchino (the earring).

Could I attach lo to the end of the sentence instead?

Yes! When using a modal verb like dovere with an infinitive (descrivere), the pronoun can go before the conjugated verb (lo deve descrivere) or attach to the end of the infinitive by dropping its final -e (deve descriverlo). Both are completely natural.