Sorry for the confusion. We can't really document the JomSocial field creation process as that's not our extension. They can change that as they want and we work with many other extensions for importing profile data, so documenting how each works would be overly cumbersome.
However, we can definitely try to improve ours. Right now, JLinked takes the huge amount of fields available from LinkedIn and tries to boil them down to more useful cases (and ones that would fit in a normal field). Our system isn't perfect, but (hopefully) works well. There are some improvements in the works. As for field documentation, you can see LinkedIn's page with information on the fields available. I'll warn you know that there's a lot of information there and it's not terribly pretty:
developer.linkedin.com/documents/profile-fields
If you have suggestions or other recommendations on how to improve, just let us know. We'll definitely look more into our documentation and see how we can make things a bit better as well.
Thanks,
Alex