Since its initial announcement, Dragon Ball Z: Kakarot has revealed 9 playable characters, including Goku, 3 different versions of Gohan, Piccolo, Vegeta (and his Majin form), Trunks, Vegito, and Gotenks. Each of these have chronological restraints, however, as players will not see Kid Gohan during the Majin Buu saga or Vegito during the Frieza Saga. As such, some characters will get less time in the sun than others such as Vegito due to his late appearance in the Majin Buu Saga.
Trunks will be playable in Dragon Ball Z: Kakarot, first appearing in his own short titular saga after the beginning of the Android Saga and playing a minor role in the story through the Cell Saga. It stands to reason that the character, due to his timing in the game and his overall popularity, will see him get more screen time than characters like Vegito, who though as equally popular, has less time during the core anime. However, how much can players still expect to see Trunks in DBZ: Kakarot?
From the get-go, it seems likely Trunks' introductory fights remain the same to some degree, with the future Super Saiyan quickly dispatching King Cold's soldiers, Mecha-Frieza, and King Cold himself. There's likely to be some cutscenes, but at one point, Trunks reveals Goku will arrive in 2 hours. This would be the perfect segue for sidequests, allowing Dragon Ball Z: Kakarot players to stretch their legs as Trunks before traveling to a spot where Goku arrives.
Once there, Trunks tests Goku's strength before revealing his identity and purpose, which may or may not manifest into a full-blown fight for Dragon Ball Z: Kakarot. After Trunks leaves, it's unsure how the 3-year wait will play out, but there's a good chance that players will get to spend some time training as Goku, Gohan, Vegeta, and/or the others before beginning the Android Saga in full.
After the Z-Fighters defeat Androids 19 and 20, and Trunks warns them that they're not the androids he was talking about, Android 17 and 18 enter the fray. His next canonical fight is Android 18, which is then followed by semi-perfect Cell when he tries to absorb 18. Vegeta intervenes, with the two Saiyans fighting as Vegeta wants Cell to power up in order to prove himself, but not to much avail. Eventually, Cell achieves his final form, defeating Gohan, Android 16, Android 18, and Trunks in the process, later on killing this version of Trunks.
After everything is said and done, the dragon balls in DBZ: Kakarot (and the anime) are used to bring everyone back, with Trunks returning to his timeline to defeat his own Android 17, 18, and (eventually) Cell. There's definitely some confusing timelines here that won't likely make it into the game, if for no other reason than to make it simple, but either Trunks returning to the future will be his last fight in the game or will appear just as a cutscene, making his loss to Cell his last fight in the game.
Either way, it appears that Trunks will likely play a major role in Dragon Ball Z: Kakarot, as he has far more potential to appear than characters like Gotenks and Vegito. What's more, Trunks will also have more time for sidequests and training, as there is a lot of down time in the Android and Cell Sagas, a strange fate given the world is at stake. Ultimately, between his canonical appearances and the high potential for sidequests, players should plan on spending a solid amount of time as Trunks.
Dragon Ball Z: Kakarot releases January 17, 2020, for PC, PS4, and Xbox One.