Normal Blackrose Prison, Stage 1, Round 2. Kill everything in the first two waves, kill the archers in the final wave, then die to the Dread Knight. Rinse and repeat.
Keep doing daily crafting writs and stockpile master writs; once you have a bunch, you can do them all at once (use an addon to autocraft everything), pop an exp scroll, and turn them all in. Great time to also powerlevel a bunch of your abilities too.
Basically, you need dense mobs. Public dungeons, Spellscar etc. XP scrolls or Psyijic Ambrosia |not both) stack with event bonus. Enlightenment accelerates the conversion of XP to CP, but you can't affect the supply of enlightenment, so it's not a factor in the grind choice.
I'm undecided on the use of Training trait gear. The bonus of XP gain per kill may be offset by the loss of DPS to make the kills.
Normal Blackrose Prison>Craglorn skyreach>Craglorn Spellscar
nbrp is best farm exp
skyreach is 2nd exp and best farm fighter guild lv but need group reset
Spellscar..not need group reset