By talking to people on a regular basis?
This problem isn't new and even affects open source. Which people in the Linux kernel are experts on which USB drivers? You can look at commits, but that doesn't always reflect the reality on the ground of the people with the actual understanding of the detailed bits of the hardware. Unless you sit on the mailing list and chat server for a couple weeks, you won't figure this out.
Big companies used to have this problem all the time back before ubiquitous communication. Some group would need knowledge about Subject A. They would appoint Person B in the group to be the liaison with Expert C who was in some other division--they would have to talk on the phone, fly to the the other division, etc. to maintain that knowledge Over time, Person B would become the "local" expert and would probably become a global expert as well. How would you find out who the experts are and where they are? You would tap your network and start walking it.
Humans network--that's just how they are.