Things You'll Need
Instructions
Change the other four characters in your party to the jobs in which you want to earn JP. For example, if you want a Knight to gain JP in White Mage, you need to have one of your party members as a White Mage.
Equip Fundaments from the Squire job as the secondary skill set for each of these characters. This is not required, but the Focus ability from Fundaments is helpful for quickly gaining JP. In most battles, enemies start outside your attack range. You can cast Focus each turn, which has no magic point (MP) cost, no casting time and no chance of failure, to gain JP each turn while you wait for the enemies to get in range.
Walk around the world map until a random battle starts. The level of enemies in random battles is scaled to your party's level, which makes these types of battles useful for earning JP.
Perform any action, such as Focus, with a character to generate spillover JP for every other party member equal to one-third the JP she earns. For example, a White Mage performs an action that earns her six JP. Her White Mage JP pool increases by six as a result. All the other party members earn two JP to their White Mage JP pool from spillover JP, regardless of what class she currently has equipped.
Win or retreat from the battle to spend the JP earned in this manner.