Well, it really all depends on what the PC's sphere of influence is going to be, I think. We have two examples of confirmed Intellectus from the novels: Harry on Demonreach, and Shagnasty causing fear and pain. Shaggy's is essentially just knowing the best way to do it without knowing why, and so Inexplicable Knowledge seems to cover it fairly well, but that is the only one I think you can model purely on Knowledge. Harry's style is a much bigger powerup, limited only by the geographic location. He has used it for widespread knowledge, but not perfect knowledge (had difficulty telling different people apart and was able to get overloaded when enough people were all fighting on the island at the same time), but it also increased his movement to the point were he outdistanced Wampires, and gave him perfect aim with some fireball spells. Now we're talking about a serious boost to combat effectiveness, so the balance of it can be somewhat fragile.
In the case of this Anatomy/biology Intellectus, you'd need to keep in mind that it is a very limited scope but mobile ability, which makes it nearly the opposite of Harry's style of intellectus. I would say auto-successes on knowledge would work fine, but you'll want to establish boundaries very clearly. The PC could tell instantly that somebody is poisoned for example, and be able to tell exactly what its doing to the body and how fast and stuff, but would he be able to tell you that there is a rare herb that only grows on the highest slopes of the Andes that will cure it? Probably not, even if he could easily draw you out the complex molecule that would accomplish it and tell you exactly how it would interact with the infected cells. In combat, Id say his attacks could do more damage by virtue of knowing precisely where to strike, and he could probably pull out some cool and unusual effects with acupressure type stuff, but just because he knows exactly were to strike to do the most damage doesnt make him any better at actually placing the bullet there if he still sucks with guns, for example.
