This requires having one character equipped with gear that grants a full row of ten bonuses from the same elemental family. Because some of the bonuses usually only appear on high level gear, this trophy should be attempted during the endgame.
One way you could do this is by setting the corresponding normin at the lords of the land, and farming gear with bonuses from the same element. You would need to change the normin you were using to make sure you got all 10 bonuses farmed on different gear types. You might also need to farm in many different locations just to ensure you were getting the right variety of drops, and not always the same one. The process would take hours. This would be a lot easier if you had high levels on your lords so you could set 2-3 normin at a time.
A much easier way to do this is to have a lot of gald saved and simply buy every piece of gear from every shop in the game. Fuse together anything that adds more bonuses to the gear, but avoid "locked" traits on your fusions because you won't have time to grind and unlock them. After doing this, go to the equipment screen, press R2, and highlight each bonus in a row that you don't have. By pressing X on bonuses, the game will bring up a list of gear that has those bonuses. Go through each character and see if any combination of gear gives you any full rows. If not, go out, fight a few battles to refill the shops, buy a ton more gear, and try again. This method eliminates the need to think or even understand how fusion works, but it relies on luck so it's not 100% guaranteed.
A combination of the two methods could also work just fine. Farm a lot of gear with similar traits, then buy a ton of gear to hopefully fill in the gaps.
I would recommend saving your game before doing any random shop purchases so that you can revert any gald you waste. The E-Union 10 bonus is probably not worth messing up all of your gear to get.