Every quest should reward xp. Prove me wrong (protip - you can't)
No, seriously. Quests only give gold (in ammounts that are not worth effort once you have 1 or 2 good caravans) and relations (which are kinda worthless, used only for recruitment but you can easily play without those few more units). I think most profitable quest I did yet was to escort caravan and it gave me maybe a few thousand gold. Cool, but 1 caravan gives me ~1 thousand every day. Quests are just an absolute waste of time once you manage to get a steady income - and even before that it might be better to simply travel around, trading stuff.
Either just make all quests provide free SP that don't increase any skills but level your hero (so there's more attribute points and focus points), or make them actually reward skill xp.
I would strongly prefer the second option. There are many types of quests and each of them can reward something. Of course it's not possible to make perfect balance with those, but hey, that's obvious when there's a system of skills rising by being used, right?
- quests for gangs could reward roguery xp
- quests like "kill bandits" could reward scouting xp and tactics xp
- quest "find missing daughter" could reward scouting xp but also extend it to allow us to convince father to let them go after we spoke with them (maybe make the daughter worried about dad so there's a reason to go to him?), with both this and convincing daughter to come back rewarding charm xp
- quest "spy party" could reward roguery xp and scouting xp (I mean, scouting is about spotting things, it doesn't have to be solely about finding things in wild, but also noticing things in urban environment)
- quest to deliver materials to artisans and quest "artisans can't sell products" could reward trading xp
- quests to train people could reward leadership xp and perhaps also tactics xp
- quest "army of poachers" could give scouting xp
- and so on with other quests that I forgot about...
Other than quests:
- destroying bandit camps, considering how there's all this waiting till night to prepare, could reward tactics xp (also increase scouting xp for spotting them)
- having a succesful caravan should reward trading xp, just as skill description says
- obviously full xp for tournament combat, maybe also some additional for winning (shared between all types of weapons?), also increased renown reward
Sadly I have no ideas of what could fit intelligence and endurance skills, shame