I am not a fan of knowledge or social skills in RPGs. They give strange results and are usually either junk or used to hand wave some juicy jibber-jabber (whoever came up with the 3.5 concept of the diplomancer should feel bad). However expecting players to come to the table with game-world knowledge, or even the awareness of what knowledge their characters should have, is unfair.
To fix this I'm using backgrounds. Talked about them before, simple things. Everyone gets a random one that determines what they were before they came to the game, what they should know. If the player is from the College of Friends then they might recognise a wizard at the party, a gremlin catcher would have all kinds of useful knowledge about sewers, necromancers can tell how long that guy's been dead, and so on. It's vague and implied.
It's not important that we know exactly how exhaustive a necromancer's CSI skills are until we start questioning it. The questions a player thinks to ask will shape the accepted remit, the GM will feel out what's too far as things proceed. A happy level will be settled upon.
There are no grades of smartness. If the necromancer is an obvious buffoon it goes one way, if he's a committed corpse fiddler it goes another.
Further knowledge is up to the players to stumble upon either organically through play or by study. Books come with a comprehension level, roll equal or higher to get an answer out of it. Go grab the book, take a 20 minute break, try to find that page you know was in here. If you find it the GM may answer your question, if the book covers that kind of thing. Or maybe a wandering monster will interrupt your study time. A good sized book will probably do D2 damage.
It's very common to find adventurers with well worn bestiaries and geological surveys strapped to their backs.