Learn Swedish: De som vill vinna måste vara utåtriktade. - Those who want to win must be extroverted.

De som translates to "those who" or "the ones who". In Swedish, you cannot use som (who/that) on its own to mean "those who" at the start of a sentence. You need the plural pronoun de (those) paired with som to create a full noun phrase that acts as the subject.

Does the V2 (verb-second) rule apply to this sentence?

Yes! Even though the subject is long, the entire phrase De som vill vinna (those who want to win) counts as one single block in the first position. Because of the V2 rule, the main verb måste comes immediately after it in the second position.

Why does the adjective utåtriktade end in -e instead of the usual plural -a?

Utåtriktad (extroverted) is formed from a verb, acting like a past participle ending in -ad. When these types of words become plural to match de som (which is plural), they take an -e ending instead of an -a, making it utåtriktade.

In spoken Swedish, is de still pronounced as dom in this phrase?

Yes, just like when it stands alone to mean "they", the de in the phrase de som is almost always pronounced as dom in everyday speech.