I'm completely stuck in the investigation quest in Chapter II. The only suspect left is Kalkstein, all the others are cleared out. I read that, after earning the trust of Kalkstein I should go to Raymond's house where he's being attacked by assassins, but that hasn't happened. Instead there are only three options when talking to him: saying goodbye, asking about him being a detective and informing him about Vincent's innocence. I've also collected nine Sephirots and the only quests that I have are:
Game of Dice
A Lost Lamb
A Mysterious Tower
Berengar's Secret
Dice Poker: The Professional
Fistfight
Monoliths
Old Friend of Mine
Suspect: Kalkstein
Wanted
Witchers' Secrets
All in all, I haven't found anything left for me to do, I've tried all talking options many times with Raymond, Kalkstein, Vincent, Gravedigger, Shani, Thaler and some others. Is there something that I've completely missed or is it a bug maybe?

I'm not sure if you skipped Raymond being attacked, but it's just assumption. How did you cleared out everyone else? Doing their 'quests'?
Well... the simples thing would be to try all other quests - I'm not sure but... maybe one of them is part of the main plot line, aka. obligatory.

I don't know, I did all the quests that i could. I cleared out the suspects by doing their quests yes, but some where very easy to clear out, just a bit of talking and that was it. And I don't know if I skipped the Raymond attack? It just didn't happen
But anyways, I started the chapter 2 from the start and this time the attack took place and i could finish the second chapter. I guess what happened was that the Vizima Confidential quest had somehow disappeared..

Now that is weird... did you cleared Vincent before doing Vizima's Confidential? Still - glad to hear you manage to solve it, altought with restarting the game. ^.^

Probably yes, I only did the suspect quests and totally forgot about the confidential one. But yeah, I'm happy the problem got solved, thanks for helping!