Learn Spanish (Latin America): Tenemos que saber adónde huir en caso de que ocurra una paradoja. - We have to know where to flee in case a paradox occurs.

The phrase en caso de que (in case) always triggers the subjunctive in Spanish. It introduces a contingency or a hypothetical situation that might or might not happen. Because we don't know for sure if a paradox will actually happen, we use the present subjunctive ocurra instead of the indicative ocurre.

Why use adónde instead of just dónde?

The word adónde combines the preposition a (to) with dónde (where). Because the verb huir (to flee) implies physical movement toward a destination, you need to use adónde (to where) rather than dónde (which implies a static location).

Why does adónde have an accent mark if this isn't a question?

Even though there are no question marks, this is an indirect question. We are stating that we need to know the answer to the implied question of "where do we flee?". In Spanish, question words always keep their accent marks when used in indirect questions like this one.

Why is the word order ocurra una paradoja rather than una paradoja ocurra?