It gets weird:
If future Trunks' zamasu knows of Goku than future Trunks' Goku knows of future Trunks' zamasu, but any Goku only knows of any zamasu BECAUSE Trunks traveled back in time to warn him of Black. Except that Black IS Zamasu who has encountered Goku, melded with him, traveled back, saved himself and causes the future of future Trunks. But future Trunks' Zamasu only knows of Goku BECAUSE of Trunks warning him of Black, who IS zamasu who encountered Goku BECEAUSE of Trunks warning him of Black, who is Zamasa because of Trunks warning Goku of Black and so on into infinity. This implies an infinite number of Trunks continuously hopping into the past creating the same future in another timeline. Like a Camera feed filming a TV that displays its own signal.
On top of that, it becomes even more paradoxical, because the normal timeline we know, Zamasu IS KILLED, meaning he cannot go to the SDBs to switch out bodies and travel back in the past and form Future Trunks' timeline as Black.... But then what's the different between the timeline we know, that is the same as all the infinite ones decribed above except this time no future Black pops up to save his own past Zamasu!? How is it possible that there's a timeline where Zamasu is killed by Beerus AT ALL? It's like we have an infinite amount of timelines where each Trunks creates the next one, yet THIS Future Trunks seems to have breached into a timeline where Zamasu DOES actually get killed.
How the **** is that possible, Trunks broke an infinite loop when time traveling this time.
(Pun unintended.)