As far as I know, the formula for exp loss on death (in normal maps, not talking crazies like Gollux) is:
A * (1 - F - C)
A = EXP loss on death as displayed in your Ambition tooltip. Starts at 10% (0 Ambition) and goes down to 5% for maximum Ambition.
F = EXP loss saved by having an Undead on your Monster Life Farm.
C = EXP loss saved by having a Cannoneer Card
However, I've been getting some strange results lately, so I started doing tests, and things don't add up.
Has the formula been changed? Do you lose less exp if a higher level enemy kills you? Or if you're 1st job? Or whatever other variables?
Edit: ah, senility http://www.southperry.net/showthread.php?t=67261
Some of the questions I'm having now were already raised then, and not answered.