Dude, you focused on 1 sentence and missed the point.
#1 It is Your WIFE’S relationship. Stay out of it unless she asks for advice.
#2 Your wife knows her dad better than you do. Trust her.
#3 Biology does not make a parent. She believes her genetics is irrelevant to her relationship with her father. She’s probably right. Odds are that he’s suspected she’s biologically not his for a while anyway.
#4 He took the test, too. He knows. Knowing that she knows and is still seeking him out as though nothing has changed probably means the world to him. No need to confront something they both are ignoring.
#5 Your wife is a full-grown, functioning adult with a mature relationship with her father. She can make these decisions without your assistance. Quit it.
Also, if you undermine this and leak it in any way, she has every right to leave you. This could be divorce-worthy behavior.
Stay. Out. Of. Her. Relationship. With. Her. Dad.
Have you tried graphic novels? Comic books get a bad rap, but there is dialog and pictures that help you get into the story. Maybe that would help?