On Pokemon card game if weakness says x2 does that mean attacks do double damage 20 40?

Yes, if a Pokémon card has a weakness to a certain type, any attacks of that type will do double damage. So, if a Pokémon has a weakness to fire, any fire-type attacks will do double damage. For example, if a fire-type attack normally does 20 damage, it will do 40 damage to a Pokémon with a weakness to fire.