A mana cost of {X}{X} means that you pay twice X. If you want X to be 3, you pay {6} to cast Cryptic Trilobite.

Activated abilities contain a colon, such as Cryptic Trilobite’s activated mana ability and its last activated ability. They’re generally written “[Cost]: [Effect].” Some keyword abilities are activated abilities (such as cycling) and will have colons in their reminder text.

You can spend the two colorless mana produced by Cryptic Trilobite on two different activated abilities.