Do you add bonus damage from Brawn to this second attack?
I would think so. I would allow it unless it specifically says it does not receive it.
[EDIT] Having read it now, I agree it would not get the bonus dice.
I think not, because it is not a melee attack.
No. While the Talent does say it is a second attack, however it goes on to say that the dirty trick is assumed to be part of the initial attack. To me, that says it’s a single attack with a conditional Momentum Spend to deal additional damage above and beyond normal melee damage. If it required an additional action, meaning an actual Melee Attack roll, I’d say yes it would include Brawn damage modifier. However, as the Talent as written, no I wouldn’t. That said, your game, do as you will.
I agree with Dytrrnikl here. Fighting Dirty says that it’s considered as part of the initial attack and so it does X [cd] extra damage with the Stun Quality, where X is the number of ranks. It also cannot cause a Wound.
In my game, the Zamoran with Fighting Dirty has pretty much found that it’s only useful to try to whittle down any remaining Vigor, but that’s a two-edged sword: if Fighting Dirty causes the victim to fall to zero Vigor, it does not cause a Wound.
In my view, it’s a marginal talent but if you have a high Melee Focus, it’s also a cheap talent.
This would indicate that dirty tricks are most effective when used to surprise an opponent and thus be used as the first part of that “initial attack”, possibly even leaving the opponent stunned and very vulnerable to the main part of the attack and the extra brawn dice related to it. I think I would allow this as a GM with the right roleplaying to go with it. Thoughts?