Every now and then I come back to this 20+ year old game. Here's my list of essential or notable job stuff in this game. Thanks to the changes made in the War of the Lions version, some stuff is just too effortful to get IMO.
Physical Jobs
Squire
Yell / Tailwind (for Ramza, I use it for most of the game. Did you know Knives and Ninja Swords use ((PA + Speed) /2) * Weapon Stat for their damage calculations?), Move +1, JP Boost, Focus / Accumulate (very useful for grinding. In any real fight, wait for the enemy to come to you while boosting your PA). Ramza's other Ramza-only skills are good, except note that Ultima is only as powerful as a Fire 3 / Bolt 3 / Ice 3, which are half as powerful as Flare or Holy.
Unlocked: At the start
Archer
Speed Save / Adrenaline Rush (take a hit, gain +1 speed; Knives and Ninja Swords use PA + speed for their damage calculations), Concentrate (improves success % of some stuff, and makes your attacks hit at 100% if every you find someone particularly dodgy)
Unlock: Squire 2
Knight
Speed Break (speed break the last enemy while grinding so you don't have to put up with them, or just any enemy in general. Synergizes very well with Dual Wielding / Two Swords from ninja, works with ranged weapons like longbows and guns), Power Break (reduce your own characters PA to 1 and have them attack each other to grind exp and jp)
Unlock: Squire 2
Monk
Chakra (restores HP and MP for free! amazing for grinding), Stigma Magic (cure conditions), Revive. other stuff is fine shrug. Brawler from the Monk and Two Swords / Dual-Wielding from the Ninja is supposedly the highest damage dealing combo in the game, but I don't use it.
Unlock: Squire 2, Knight 3
Thief
Move +2, Steal GP (not bad for grinding, amount of GP stolen affected by speed stat! triggers an enemy counter)
Unlock: Squire 2, Archer 3
Geomancer
Attack Up (it's been a while, but I remember this boosts the damage of Holy Sword for Agrias and Orlandu)
Unlock: Squire 2, Archer 3, Monk 4
Lancer / Dragoon
Auto-raise / dragon spirit, Ignore Height (ignore height is amazing for one fight in particular in CH4, at Zeltenia Castle against Zalmour the Heresy Exclaimer)
Unlock: Squire 2, Archer 3, Thief 4
Samurai
Blade Grasp / Shirahadori (get this on someone cursewording ASAP). I don't use anything else from this class but Draw Out / Iaido skills are affected by the Magic Attack (MA) stat, so this skill set might suit a female magic character or synergize with a male character using the Bard's MA Save.
Unlock: Squire 2, Archer 3, Knight 4, Thief 4, Monk 5, Dragoon 2
Ninja
Two Swords / Dual Wield (too bad the duplicate weapon glitch was patched out), Shuriken and Bombs are fine
Unlock: Squire 2, Archer 4, Knight 3, Monk 4, Thief 5, Geomancer 2
Dancer
Too much effort for me. PA Save / Attack Save for possible niche strategies with female physical attack characters
Unlock: Squire 2, Knight 3, Archer 3, Monk 4, Thief 4, Dragoon 5, Geomancer 5
Magic Jobs
Chemist
Potion, Phoenix Down (all outdated by Monk IMO, except that Phoenix Down has a 100% success and Revive doesn't); Note that general use of auto-potion is just a good way to waste potions; specific-use only. There are better reactions for general use.
Unlocked: At the start
Black Mage / Wizard
Frog (get this asap! Frog doesn't wear off on its own. It makes a character do damage in the single digits and stops characters from casting spells. When grinding, kill off all but one enemy, then turn them into a frog so that they are basically useless)
Unlock: Chemist 2
White Mage / Priest
Cure 3, Raise 2, Esuna, Holy, Wall (all excellent for Math Skills. Get anything else and I think it clutters up the Math Skill list. Holy is cheaper and more powerful than Flare from the Black Mage / Wizard spell list).
Unlock: Chemist 2
Oracle / Mystic
Repose / Sleep is notable as a poor-man's Frog. I don't really use anything from this class, but its spells look cool.
Unlock: White Mage 3
Time Mage
Haste, Teleport (ignores height and obstacles, can increase the number of squares you can move with a chance to fail of 10% per square beyond you Move stat, so Move +1 90%, Move +2 80%, etc.)
Unlock: Black Mage 3
Calculator / Arithmetician
I think you need a dedicated magic character in your roster to learn all these action abilities. All the action abilities are essential for this classes' skillset.
Unlock: Chest 2, White Mage 5, Black Mage 5, Mystic 4, Time Mage 4
Mediator / Orator
Entice / Invitation (want to steal an NPC's gear? Just add them to your party roster instead), Preach, Enlighten / Solution, Praise, Intimidate / Threaten, Equip Gun (this is actually one of my favorite support classes although the stat growth is poor)
Unlock: Chemist 2, White Mage 3, Mystic 3
Summoner
I don't use this class or anything from it. Best MP growth (chakra and Math Skills roll eyes)
Unlock: Chemist 2, Black Mage 3, Time Mage 3
Bard
Too much effort for me. MA Save / Magic Save for possible niche strategies with male magic characters, Move +3
Unlock: Chemist 2, White Mage 3, Black Mage 3, Mystic 3, Time Mage 3, Orator 5, Summoner 5
Others
Mime
Too much effort for me / I don't use this class.
Unlock: Squire 8, Chemist 8, Knight 3, Archer 3, Monk 4, Thief 4, Dragoon 5, Geomancer 5, Chemist 2, White Mage 3, Black Mage 3, Mystic 3, Time Mage 3, Orator 5, Summoner 5
Dark Knight
I unlocked this class once. Once.
Squire 2, Knight 4 (Master), Monk 4, Archer 4, Thief 4, Geomancer 8, Dragoon 8, Samurai 8, Ninja 8, Chemist 2, Black Mage (Master), also supposedly you must kill / crystalize 20 enemies.
Onion Knight
Too much effort for me. Apparently, this class starts off poor and gets better after MASTERING all the other jobs. The exact mechanic, I've read, is the Onion Knight's job level goes up by 1 for every 2 jobs you master, and when the Onion Knight reaches job level 8, it gets some big boosts to its stats.
Unlock: Squire 6, Chemist 6
