simply put research is a standard 1d3 roll
This represents a completely uneducated person making an attempt to figure out whats going on.
investing 100gp and 100xp will gain an extra size to the dice ie
1d3 -> 1d4 ->1d5
This represents someone spending a large amount of time and money in researching the subject, even a newbie can learn valuable information like this. Though there is an increasingly small chance that they will find out nothing still.
Half the knowledge skill is invested in a roll about a specific thing within the realm of that knowledge. So if the player has discovered a zombie is running amok and they have 4 points in the "knowledge: corporeal undead" section they get a bonus of 2 to the roll.
This in real terms is the fact that a hunter with at least some experience in the field of corporeal undead is likely to do good research into the zombie and figure out at least one established way to fight it.
Knowledge skills get invested in as hunters level up and can be considered to be a mark of how much they have experience facing the supernatural in specific areas.
It seems like a lot at once, but the most the bonus you will receive on the roll is likely to be is a +4, and only the most experienced hunters are going to get that.
Some particularly powerful and obscure nuggets of information are incredibly hard to find out and require extreme research into the subject. As such some information will only be revealed on very high rolls.
Basic information might encompass ways to repel or hurt a monster would be the kind of facts you'd learn for a 3/4/5 roll
Advanced information might involve things like sigils and markings that can be used to draw out or trap monsters would be the like you'd find from getting a 7/8/9
Rare information would have incredibly powerful effects, like perhaps a power word which repels the creature or a method which will quickly and effectively kill the creature as opposed to more difficult methods less fruitful research will leave.
Finally a small example roll.
Carroll Gunnman is a 5th level hunter.
He has 8 points invested in "knowledge:fey"
He has been tracking what he thinks is a dyrad, however when he got into combat with it, his usual method of dispatching dryads, a burning stake to the heart, had little effect and he barely escaped with his life.
He decides to research the subject.
He decides to spend 100xp and 100gp on research and has a knowledge bonus of 8 for fey.
Therefore his total roll is 1d4+4
he rolls a 2 giving him a total of 6
From his research he has learned that dryads grow stronger the longer they are left in a place of woodland antiquity, eventually they will become a dryad matron, a powerful dryad that can convert virgin maidens into dryads. This is a grave threat but he has also learned that a dryad matron can be reduced in power by burning her source tree. Doing so will allow him to stake the dryad as normal and end its reign of terror.
He will have to figure out its tree by himself however, as he found no way to indicate how to tell if a tree is a source tree.
That was a long post, did that make sense? I hope so :S