How do you get two charged attacks at once on a Pokemon in Pokemon GO?

Question

I don't want to know how to switch the charged attack, but to have two options at once while battling.

Answer 1

Source: Bulbapedia

The player can also spend Stardust and Candy to teach a Pokémon a
second Charged Attack. Upon evolution, both Charged Attack will be
randomly reselected. Caterpie, Metapod, Weedle, Kakuna, Magikarp,
Ditto, Wynaut, Wobbuffet, Smeargle, Wurmple, Silcoon, Cascoon,
Taillow, Feebas, Beldum and Kricketot cannot learn a second Charged
Attack.
The cost varies depending on the Pokémon species and largely
corresponds with the distance needed to walk for a Buddy Pokémon to
find a Candy. In addition Shadow Pokémon, compared to their base
forms, requires 1.2× Stardust and Candy to learn a second Charged
Attack, while Purified Pokémon require 0.8× the base amounts.

The option to teach the second charged move is on the lower part of the Pokémon's summary screen. It can cost quite a lot of stardust and candies dpending of the Pokémon.

Hope I helped!