Learn French: Tu préfères l'Océanie ou l'Asie ?

In French, continents, countries, and regions generally require a definite article (le, la, l', or les). While in English we just say "Asia", French requires l'Asie. This is especially true when they are the subject or direct object of a sentence, or used with verbs of preference like préférer, aimer, or détester.

Would I still use the article if I were saying "I am going to Asia"?

No, and that is a common trap! When you use a feminine continent or country with the preposition meaning "to" or "in", you use en and drop the article. So, "I prefer Asia" is Je préfère l'Asie, but "I am going to Asia" is Je vais en Asie.

Why does préfères have a grave accent (è) when the infinitive préférer has an acute accent (é)?

Préférer is a stem-changing verb. When the verb is conjugated and the final syllable is silent (like the -es in tu préfères), the é in the stem changes to è so the vowel can be pronounced clearly. For forms where the ending is pronounced (like nous préférons), the accent stays é.