I've had this discussion in a few places elsewhere but there are a lot of moving parts to it. I don't really have one single question about the subject but I'd like to see if someone sees a flaw I missed in my interpretations or just if someones has different ideas.
This is a relevant thread but it's from a time with a lot less options (just the inventor's weapon modifications completely turns it on its head).
So trip, grapple, shove and disarm are not attack rolls but are attacks (plus force open and escape, I forgot about these until I double checked while writing this post). Usually strike is the only attack that deals damage but not always.
Without any feats, trip deals 1d6 damage on a crit.
Force open may deal damage to an object.
With feats, crushing grab and brutal bully add a damage component to some non strike attacks.
Harder they fall also does but with a different wording that closely mirrors the trip crit success.
We know a maneuver executed with a free hand is an attack but not an unarmed attack. However there are both weapons and unarmed attacks with maneuver traits (ie: dhampir's fangs and fangwire), which presumably makes weapon attack maneuvers and unarmed attack maneuvers something possible (I've been told on another site that this isn't the case but no explanation for why that was so feel free to give your opinion on that).
We know for sure that none of this damage is a hit (that's a keyword for a success on a strike) nor a damage roll (ditto).
Most additional damage effects are worded to add damage on either a hit (ie:corrosive weapon) or a damage roll (ie:twin weapon).
However there are a handful of stand out effects that are worded differently.
Enlarge gives a status bonus to melee damage.
Forceful gives a circumstance bonus to damage equal to the number of weapon damage dice on an attack (not a strike).
The weapon specialization class feature (shared by classes but not identical) gives additional damage with weapons and unarmed attacks.
We should pretty much agree on everything so far unless I've misunderstood something very basic. That being said here's how I'm interpreting it:
Additional damage/status bonus to damage requires damage to be dealt in the first place to be applied (except when using Certain Strike but that's not relevant now since it's a strike).
Crushing grab and brutal bully modify the maneuver they apply to and make it a source of damage, if they weren't they would be a free action instead of a passive effect. Crushing grab also calls itself an attack "You can make this attack nonlethal with no penalty."
Crit trip and harder they fall might not be the same as crushing grab and brutal bully. The former say "the target takes dmg" while the latter say "you deal dmg". I believe this is meant to represent hitting the ground, not damage dealt with the implement used to trip.
Because of this I think forceful and weapon spec add damage to brutal bully and crushing grab but not trip or harder they fall.
I believe Enlarge adds damage to all 4 of the situations, as it has the broadest wording (bonus to melee damage).