Joachim told Khan right before the final battle the Wrath of Khan how starships are affected by nebulae. This was about when Admiral Kirk taunted Khan into following him into the Mutara Nebula where the wounded Enterprise would be a match for the Reliant.
Joachim: If they go in there, we will lose them.
That means he knows that none of the Reliant's sensors could detect the Enterprise inside the Mutara Nebula.
Khan: Why are we slowing?
Joachim: We can't follow them into the nebula, sir. Shields would be useless.
How did he know shields are inoperative inside a nebula?
Khan: Raise the shields.
Joachim: As I feared, sir. Nonfunctional.
This is all very specific knowledge about space combat involving the technology on Federation starships inside certain types of nebulae. It's also the kind of knowledge that is best learned from direct experience. Neither Khan nor his followers had much experience in space combat.
How did he know that?
Please provide answers based on canon sources.