What does Genesis 46:20 mean?
All the currently living descendants of Jacob are being listed, grouped according to the wife that bore them. Now the list comes to Joseph, sold into slavery in Egypt by his brothers many years earlier (Genesis 37:24–28).When Pharaoh made Joseph a ruler in Egypt (Genesis 41:44), he gave to Joseph a wife from a prominent Egyptian family. Asenath was the daughter of a priest of the god On. She bore two sons to Joseph—Manasseh and Ephraim (Genesis 41:50–52). Joseph named Manasseh in honor of God who helped him forget his earlier suffering. Ephraim is named in honor of God who made Joseph fruitful even as a slave in Egypt.
These three, Joseph, Manasseh, and Ephraim, were already in Egypt when the rest of the family arrived.