Learn Spanish (Latin America): ¿Cómo supiste dónde enterrar el tesoro? - How did you know where to bury the treasure?

Supiste is the tú (informal you) form of saber (to know) in the preterite tense. Saber is highly irregular in the preterite: it changes its stem completely to sup- and uses a special set of endings without any accent marks.

Wait, doesn't the preterite of saber mean "to find out"?

Yes! In the preterite tense, saber usually implies a sudden realization, meaning "found out" or "learned" a piece of information, rather than ongoing knowledge (which would use the imperfect tense sabías). So, this sentence is essentially asking "How did you find out where to bury the treasure?"

Why does dónde have an accent mark if the main question is already started by ¿Cómo?

Question words like dónde (where), cómo (how), and qué (what) always keep their accent marks when they introduce an indirect question or an unknown variable inside a sentence. Even though the main question starts with ¿Cómo, the word dónde is still acting as a question word here.

Why is enterrar in the infinitive form rather than conjugated?