When Is a Good Time to Start Using Ancient Knowledge Scroll

[WhYdOyOuThInKtHaThApPeNeD]

Clear the way of any ordinary fight/enemy encounters leading to access the boss battles: Driller, Frog & Spider. Use Ancient Knowledge then go for those fights in a row (of course having saved them till ready), they give the most XP of any fight.

The best hero battles accessed mid game for the last 2 uses on the scroll are (xp given is what I got when I played them on normal):

Fangol (7535 xp w/ scroll)
Hagni (5472 xp w/ scroll)
Hogan (4604 xp w/ scroll)
Demenion (9,671 xp no scroll, 13,554 with scroll)

Accessed usually a bit later:

Gremlion (29,921 w/s)
Uchkuk (9259 w/s)
Shenobi (13,505 w/s)
Defense Diploma on Elon (6983 w/s)
Rakush (5097 n/s)
Urh-Urh (4574 n/s)
Rakatarh (4650 n/s)


I think these are on Reha, the arena challenges)
Ziraks (15,016 w/s)
Harrum (13,069)

K'Tahu (37,401 w/s)

Should give an idea where to best use the Ancient Knowledge scroll.

As MaroonMaurader said, if any of your living items are getting low on morale suppress them before you activate the scroll since item battles use up an AK scroll.
As DGDobrev said, Nameless, Sheterra & Reha have the battles that give the most XP in the game.