1)He's a necromancer. He summons, consumes, binds and manipulates ghosts and spirits. The more he knows about an afterlife the better he is at manipulating it, drawing power from its denizens, or making deals with its rulers and natives.
We do not want to enable him by improving his knowledge of the Thousand Hells.
2) No thats not how it works in the Dresdenverse.
Actual magic knowledge is usually controlled or obscure and the really hard stuff is often rare. Much of the plot of Dead Beat involved a scramble for the only copy of an ascension ritual in Chicago, and Dresden figuring out the nature of the Erl King.
We have an Ages-old spirit in our head with knowledge thats rare.
If this sort of thing was easy to find out, Gorfel would already know it. He's been a sorcerer for longer than Michael has been alive, and he can summon spirits for information.
3)If he gets taken to Edinburgh and successfully interrogated before execution, everything they get out of him is accessible to everyone senior enough to get the interrogation records or who has the magic powers to listen in.
That includes Odin, the Archive and Anduriel of the Fallen. And everyone that Nemesis has subverted.
4)There is a spirit of rage in Gorfel's head, giving him superhealing and possibly listening to every conversation.
If dude dies, said spirit goes back to its bosses.
With everything its overheard and remembers.
5)Gorfel operates in Chicago and recognizes Michael on sight. I think he knows damn well that Molly is his daughter.
Dude probably knows the face of every one of Michael's children; its public knowledge, and accessible to anyone willing to hire a private investigator to spend thirty minutes at the public birth records office and two hours outside the Carpenter home on Sunday with a camera.
Its not a good idea to assume incompetence on the part of our opposition. Hostiles who know enough about the ongoing working relationship between Michael and Harry to ambush us outside his home, and who have the resources to put a marksman on site at short notice can be assumed to have done their basic homework about local Chicago persons of interest.
=========
The breadth of our knowledge is indicative of our powers and specialties, and it allows people to prepare for us. Which we do not want. OOC, we know the Bad Guys have moles in Edinburgh and many other places. IC, we know that Molly has survived against fetches, Red Court vampires and Outsiders because she's an OCP, and her survival is better the longer it stays that way.
A successful interrogation attempts to extract as much information as possible without giving any away, because any and all information will be used against you by enemy wizards.
.
