I have gone over an hour killing the same mob and not gotten knowledge to "drop" it's just bad luck. When I go hunting mobs I missed for knowledge I tend to just expect to need around 100 kills, that way I'm not too upset when it takes longer (usually it doesn't but sometimes it has). I had to destroy over 80 of those skull piles yesterday at the corrupted farm outside of Calpheon to get the knowledge (8 spawn at a time, I did more than 10 rounds of killing them, then waiting for respawns). Took about 100 crows in that same area to get the knowledge to "drop". And then I spent about 75 minutes blasting Keplan Catapults at the Oze mines area before I got the knowledge. I had over 140 of the little turn-in items they drop, and the drop rate isn't 100% on those, just to give you an idea. Basically RNG hates me and it it must have something against your wife, too.