Thats an interesting question. We know that soul reading will be a thing in the future but dont know anything about manifesting.
I bet that if it is possible it would be juat like when Shallan(or another Radiant) is peeking into Shadesmar. When she does that her soul flame is manifesting into "a version of her soul" in Shadesmar.
Maybe if someone tried to manifest a person, it would pull them partly into the Cognitive Realm like when Shallan is peeking
https://wob.coppermind.net/events/117/#e1597
