Learn Russian: Кое-кто скрывает правду, но через неделю мы её узнаем. - Someone is hiding the truth, but in a week we will find it out.

Кое-кто usually means the speaker knows exactly who is hiding the truth, but is choosing to be secretive and not name them right now. If they used кто-то, it would mean some unknown person is doing it.

Does кое-кто always take a singular verb like скрывает?

Yes. Because it is based on the question word кто (who), it is always treated as grammatically singular (and masculine in the past tense), even if the speaker actually has multiple people in mind.

Why do we use через to say "in a week"? Doesn't it usually mean "through" or "across"?

While через does mean "through" or "across" for physical space, when combined with a period of time in the accusative case (like неделю), it is the standard way to express "in" or "after" an amount of time.

Why does the sentence use её (her) to say we will find "it" out?

In Russian, pronouns must match the grammatical gender of the noun they replace. The word for "truth" is правда, which is a feminine noun, so it must be replaced by the feminine accusative pronoun её.

What is the difference between узнаем and знаем?