Hmmm, I would probably impart to them the basics and divulge more on case by case basis as they gain more levels.

For example, a low-level Ranger might get, "You recognize the creature as Y, an otherworldy abombination," whereas if a mid-level Ranger found a clue, "You recognize X clue as indication of Ys in the area, an otherwordly creature from Z," whereas a high-level Ranger would likely get almost all relevant info from the entry, including any strengths and weaknesses.

Sometimes a low-level Ranger might get mid-level info or mid-level might get high-level info depending on the situation, like if they'd fought one before or were seeking one as part of a mission (basically, a reason to have studied them more specifically during training).

If a more generous ruling seems to heighten the excitement of the moment or if the player did something creative as part of the inquiry, I would probably also lean toward more over less. I generally enjoy a chance to let a PC's special ability shine.

Sounds like a good opportunity for d6 task resolution.

Iron Ranger wrote:

Given the specifics of the text, I give all Rangers complete knowledge, as the training is not only thorough in identification but to understand their weaknesses, one could reasonably assume the study of all its traits and habits necessary.

I'll have to read it again - I was going from memory. Don't want to shortchange them.
 

Thanks for all the responses.  I will likely give the character knowledge of various powers but the alien agenda would preclude them from knowing exactly when, how, and why they would use them.