As the description says, this is for gaining Tier 9 in certain spell circles. It actually has nothing to do at all with *learning* spells.
The circles are divided into two groups. The elemental circles and the effect circles. The elemental circles are as follows: Fire, Water, Air, Earth, Death, Life.
Tier 9 is the max tier level for a circle.
There are two ways to gain circle tiers: 1) in Lord creation - a custom Lord can select circles and tiers to start the game with (the total tiers is limited) and then 2) Many types of landmarks scattered around the map grant a spell circle as one of many random rewards. That spell circle reward is +1 to the circle's current tier level.
The way I did this was starting with a custom Lord with all points pumped into elemental circle tiers. I set up 3 planes/Pangea/Land Mass: 90%/World Size: Large/Features: Countless/Single Opponent/Everything Else: Default. Then for the fighting, I simply saved before each Landmark fight and reloaded if I didn't get a circle I needed. The rewards are not preset and randomize with each battle. Thankfully, the game also notes the circles you've got whose tiers are maxed at 9 and stops offering them as a reward. I also noted that the difficulty of the encounter seemed to impact the chance of getting a circle as a reward. Higher difficulty fights generally always grant a circle. Super easy fights very rarely grant a circle. Unfortunately because of this, I ended up fighting as many difficult encounters as I could find to increase the circle drop rate. The game's auto-battle system is unbalanced and broken imo, so I needed to do these difficult fights manually making this trophy tedious.
Also note, the trophy did not pop immediately. It took a couple minutes (like many trophies in this game)