25 pieces of knowledge can be obtained, duplicate knowledge can be obtained.
Only worth going for the guaranteed knowledge when the chance to obtain new knowledge is less than 10%.
This means when you have 2 out of the 25 left to obtain, 2/25 = 8%.
Expected attempts to obtain new knowledge goes up with each one obtained, 25/25 + 25/24 + 25/23 + ... + 25/3.
This sums to be 57.899..., you can then add on the 20 runs needed for the guaranteed knowledge for a total expected amount of runs to be approximately 78 runs.

I think this is the minimum average number of runs that it will take to get all the knowledge. I hope they make it a bit easier, maybe increasing the number of scrolls per run to 2 would already be a great improvement. GL

While the above calculations are accurate, this implies that you have at least average rng.

In my experience doing these, you should consider doing the 10 scrolls exchange for guaranteed knowledge when you've got about 4 or 3 left. Definitely at 3 anyway.

FTR if you do the solo runs, you can do the boss over and over for one scroll without ever exiting, just take the teleporter to the left that is against the wall in the boss room which takes you back to vaha's garden, then take the teleporter in the middle of the room there that takes you back to vaha's cradle/boss room and use the dagger to spawn him again. It takes give or take an hour to do 20 runs.