FINAL FANTASY XV POCKET EDITION HD

Easy AP farm.
Credit to Throni360.

1. Start Chapter 6 Callings,
2. Skip all the boat dialog and land on Altissa, then game will create a map autosave,
3. Start collecting all 6 hidden cactuars, there are 3 on the Leville Station, 1 at the Ministerial Quarter Station and 2 at the Floating Market Station - Maagho, leave the cactuar next to the bartender for last.
4. Speak to the bartender to clear the main objective and get an autosave,
5. Quit to the overworld and quit the game from there,
6. Select load and to the left of your save file is a pink button that will reset the current chapter you are on, this in turn will reset you to when you disembark from the boat skipping the boat dialog,
7. Repeat step 3 through 6.

Doing this will grant you 12 AP each time, no battles needed just some running around. Another benefit is that just by doing the cactuars and the unavoidable wedding dress sidequest you will gain a small amount of XP that also does not reset, so about a couple of runs you can get to a level up screen and cash in for extra levels and more AP, then reset the save file to do more grinding.

personally I did this technique in episode 6.that reports 12 ap in about 4 minutes after I think there is a faster method

Just keep grinding AP until you unlock all of the ability nodes. I believe this must be done on one save file. It seems that on Windows and mobile versions you could spread it out over multiple saves but it was changed for the console releases. Also, you must have all of the Royal Arms in order to have all ability nodes available.

I played all the way through the game then grinded on Chapter 6 (Leviathan trial) to get the rest. You can easily get between 40 and 50 AP by doing this chapter. You get 2AP for each Cactuar statue (there are six) and you get more by leveling up your characters and there is quite a bet of XP to be had in this Chapter. My Noctis is level 72 and I still level up at least once during this chapter every time.