If you have Scholar and talk to him you can challenge him to answer a question and he will then ask you questions, answers are:

Lucian parted from us in 1233, Tenex was first king of the Dwarves, Cassandra was Bracus' twin. He will then invite you to join him in his private chambers. Talk to him again and he asks what's the most amazing thing you've discovered? I replied about the Gods but it could be any one of the 3 options.

Rewards were Summon Fire Slug (as a wizard starter so I assume it's your primary class 1 source point book), 2960 gold, 1 giant venom rune, Wonderous Wraps and a choice of a single 1 source point ability skill book from all of them. Summon Fire slug was in there too which makes me think the guranteed one is based off of your primary class.

Wonderous Wraps are Divine hand armour. At level 20 they gave 280 magic armour, 391 physical armour, +10% Earth resistance, +1 Telekenesis, +2 initiative, +282 hp and granted skill Restoration.

This was also never marked as an actual quest and just found via diaolgue.

House of dreams is the answer to that question

Can you kill him without breaking any quest or something? For XP...

I chose arcane stitch as my reward and got arrow spray, fan of knives, meteor shower, skin graft, and grasp of the starved after looting his basement (some in bookshelves, chests and desk) Im not sure if it was just coincidence but those are almost all the books he offered as rewards excluding Chain Lightning

Where is his safe for the key you can loot in the loose board in the small room with the locked door?

Has ayone managed to get all of his books BEFORE speaking to him for the first time ? I would suggest some hidden dialogle or something there - i couldnt do it, i collected all and was still missing like 5 (randomly it was book nr 5, 10, 15. 20, 35 from him - i had all others but for those 5 but that was (ofc) not enough