Basically the what the subject title says. Where can I edit the amount of XP you get when defeating an enemy? I'm guessing either Statblock.cpp, LootManager.cpp, or Avatar.cpp?
In the current dev version (not in the last binary release) you can specify in each enemy definition file the XP rewarded like this. E.g:
xp=100
Later we'll also allow defining a default XP amount for each enemy level, but that's not in yet.