Can be found in the info panel.
For now, you can only see your own renown.
It might be wiped again if there is an error in the calculation.
Also, it is only visual, although it is quite likely to change in the future and enable the player to do more (eg more troops, more goods, etc).
Renown = item value lost by both sides together
25% goes to the attacker/defender.
75% get split up on the faction (every member).
It's planned to give renown for other stuff too, like trading and fighting as a merc. This must be evaluated first though. I am open for bribes to think in certain directions.