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



×2
Dig Claws
EarthquakeThis attack also does 10 damage to each of your Benched Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
The spikes on its body are made up of its hardened hide. It rolls up and attacks foes with its spikes.
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.