Earthquake is TM26
No, Darkrai is not able to learn Earthquake.
Gastrodon does not learn Earthquake naturally, but it can learn it through use of a TM.
Yes, Gallade is able to learn Earthquake through the use of the Earthquake TM.
metang doesnt learn earthquake.
Aggron can learn earthquake by using the TM on it.
Yes, it can learn it by using the TM Earthquake
Nidoking can only learn Earthquake when you use TM26 on it.
It doesn't learn Earthquake through level up, but it can learn it through the use of the Earthquake TM.
Venusaur can only learn Earthquake through TM26 Earthquake.
Rampardos can learn the move Earthquake though not by leveling up. You can teach Earthquake to Rampardos by using the TM 26 on it.
Get rid of Sudowoodo
Numel does not naturally learn Earthquake in its movepool. However, it can learn Earthquake through TM26 in Pokémon games, starting from Generation III.