Also, I THINK that the Death Attack gets automatically applied to the Sneak Attack, so you wont see 'Death Attack' on screen.
From
Death attack: - NWN2Wiki
At 1st level, the assassin can make a special sneak attack called a Death Attack. This functions exactly like rogue's sneak attack ability, except that the attack has a chance of paralyzing the target. The assassin's Death Attack inflicts an

extra

1d6 points of damage. This bonus rises to +2d6 at 3rd level, +3d6 at 5th level, +4d6 at 7th level and +5d6 at 9th level.