All guild quests (including those started within character routes) should be giving you EXP, as well as killing any creature (both within guild quests and outside of them). If this isn't happening, you'd do us a favor by joining our discord (https://discord.gg/ZZ79sMT) and reporting which quests don't give EXP in the #bug-report channel
Viewing post in Randel Tales: Act 1 [Premium] comments
I had to grind a bit xp too. (But I suspect this was only because I did only girl quests. I do expect some boring elements to be in the game, that only highlights the good parts.) Another mention is Twig, elf village and Cynthia routes. I had to see walkthrough (and see sex scenes in the gamefiles) because I had no idea which would trigger them. Minor tracker issue is all.