I'm reading Rash"i's explanation n Breishit 43:14 explaining the part of the verse:
"May he send you your other brother..."
Rash"i says that a holy spirit caused him to include Joseph in this request.
This seems to imply two ideas - that Joseph was alive (The Torah indicates that Jacob said "a bad animal ate him" and that he mourned over him. It's unclear if that implies that he believed that the animal killed him, though.) Did Jacob believe that Joseph was alive, and who / what convinced him?
The other question is that assuming that he believed he was alive, what made him think that he may be in Egypt?