I think it would be cool for rangers to have a little tool to check creature type in-game. That way if you decided in-character during play that you wanted to focus against a particular creature you encountered, the player could know unambiguously what type to select next time they get a favored enemy selection.
If this isn't possible I think it would be reasonable to post a list of creature types for players to access. But I like the idea of encountering them first in-game then deciding to focus against them.