Since Jabba had a bounty on Han, it would make sense that Luke would assume Jabba would be in possession of Han. Luke probably still had connections with people on Tattooine, people who could have been doing business with Jabba, thereby passing Han's whereabouts back to Luke. Didn't seem like it was any big secret since Han was proudly on display in Jabba's throne room.
Reply by Jan El Señor
on November 12, 2017 at 9:31 AM
It's implied that they tracked down Han's location in between the films.
Reply by MirrorUniverse
on November 12, 2017 at 11:09 AM
At the end of Empire, Lando told Luke he and Chewie were going to find Jabba, so they must've found out before the movie ended.
Reply by Dark_Sithlord
on November 13, 2017 at 1:24 PM
Since Jabba had a bounty on Han, it would make sense that Luke would assume Jabba would be in possession of Han. Luke probably still had connections with people on Tattooine, people who could have been doing business with Jabba, thereby passing Han's whereabouts back to Luke. Didn't seem like it was any big secret since Han was proudly on display in Jabba's throne room.
Reply by tmdb43737777
on November 14, 2017 at 6:36 AM
I never about it like that. It would make sense that someone could've seen it and passed it on