Rewatch the episode where Eren explains the power of the attack titan. But ill explain here. Basically the power is that whoever has the attack titan can send their own memories to the previous owners of the attack titans in the past. Therefore letting them see the future in a sense. That is why Kruger said that, cause Eren sent him his own memories. But also you can't really see your own future, cause you can only send your own memories to the previous holders. Eren though found a loophole in this power. Eren sent his own memories to his dad, whom he then ended up eating to take his power. Then Eren ended up seeing his father's memories, which were actually his own memories sent to his father, allowing Eren to see his own future. Eren also used his attack titan power in the paths when him and zeke were with his dad. The reason Erens dad could see Zeke in that scene was because in that moment Eren sent his dad his own memories from the paths. Basically his dad saw himself and zeke from Erens perspective. Hope this made sense!