He didn’t know Saturn specifically but he knew that the gorosei would have to come personally to take the pacifistas from Egghead two years. Would also explain why Vegapunk set up the hierarchy like this if it was a trap in the end.
Yes, Kuma knew 2 years in advance that CP7, CP8... wouldn't be sufficient to take down Vegapunk.
Kuma knew that CP0 would also not be sufficient.
More surprisingly, Kuma FORESHADOWED that Kizaru wouldn't be able to kill Vegapunk because of Nika's presence in Egghead.
Even more intriguingly, Kuma knew that Saturn would accompany Kizaru and that Saturn would land on Egghead after Kizaru fails his mission.
Kuma certainly has an advanced form of future sight /s.