What magic would we be looking into if we wanted to learn more about how souls work?
Shyish has some soul stuff, because it's the Wind of Endings and there's no bigger ending than death and your soul leaving your body, but of course we can't use it without going stark raving mad. By extension of being corrupted Shyish, Necromancy has some soul stuff too, which Mathilde knows a bit about in theory via the Liber Mortis. But it would just be theory, and I'm not too keen on learning the differences in practice.
Some cults such as that of Morr would have stuff on the soul, but they would be
extremely tight-lipped about them, because it'd be divine secrets concerning something extremely sacred.
It was floated as an idea to ask Gunnars to learn more about Gazul because he also is concerned with safeguarding souls, but it's not a guarantee that there'd be anything applicable to our own research in this general subject - IIRC the only thing
guaranteed (beyond getting the Gazul skill to Basic) is rites to protect tombs from intrusion (even very heavy intrusions). There's also been a lot of discussion surrounding the overall idea anyway - some people including myself would rather take such actions to actually know more about Gazul in general, not with an expectation of a 'reward'.
And finally, I think Hedgecraft miiiiight have something on the soul, given that their magic is concerned with a lot of conceptual boundaries and the soul is something that is part of the Aethyr despite residing in reality.