I can't find the answer to this anywhere. For shatter defenses, if another character in your party dazzles something, and other characters in your party have "shatter defenses," do they do the extra damage as well? Or does only the character who dazzles the enemy do the extra damage? It seems common to add shatter defenses to almost everything, but the game's descriptions aren't clear.
Shatter Defenses doesn’t deal extra damage (it doesn’t claim so anywhere in its description either). It makes the opponent flat-flooted which makes them easier to hit, since they lose a lot of bonuses to armor class.
It’s also not about Dazzling (a condition that has nothing to do with Shatter Defenses) - I presume you’re talking about using the feat Dazzling Display, which causes the Shaken condition. But any fear condition can proc Shatter Defenses (Shaken, Frightened, Panicked), no matter the source (Dazzling Display, Intimidate, a spell, whatever).
The fear can come from any source, but Shatter Defenses only works for the character using the feat. So this is it how it works:
1) An enemy gets Shaken, Frightened or Panicked from whatever thing
2) You, a character with Shatter Defences, hit that enemy with an attack
3) That enemy is now flat-footed against your attacks until the end of your next turn, meaning it loses its Dex, Dodge bonus etc. to AC (and if you are a rogue, you can now sneak attack the target freely). This is only against your attacks, but if three party members have Shatter Defenses they can all proc Shatter Defenses for themselves.
That’s how it’s supposed to work. How it actually works in my experience is that if you have Shattered Defenses your attacks treat any Shaken, Frightened or Panicked enemy as flat-footed automatically, which is quite dumb but then that’s Owlcat for you. In order to put six billions feats in the game they compromised heavily on implementation, so things are still b0rked to this day.