Can Walking Wake's Ability be used against Cornerstone Mask Ogerpon ex 112/167 Scarlet & Violet?

Walking Wake ex ability Azure Seas's effect is the same as Shred, Azure Seas simply applies it to any attack Walking Wake ex uses.

So yes, it goes through Cornerstone Mask Ogrepon... not only that but anything that the opponent's Pokemon can do to try to reduce or nullify the damage will not effect on Walking Wake’s ex attack.