If I have a Tera Pokemon on my Bench when I use Landorus' "Earthquake" attack, do they take 10 damage or not?
No, the Tera Trait protects them from damage by your own attacks as well.
Earthquake





x2
Eerie FluidYour opponent's Active Pokémon is now Confused.


EarthquakeThis attack does 10 damage to each of your Benched Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
If I have a Tera Pokemon on my Bench when I use Landorus' "Earthquake" attack, do they take 10 damage or not?
No, the Tera Trait protects them from damage by your own attacks as well.