Can this be translated as "Who will believe him?"
no, it can't. it's very difficult even to an Italian native (I lost a heart).
"chi lo crederà" who will believe that
"chi gli crederà" who will believe to him
I think this would be: "Chi GLI crederà?".
"Lo" can be translated as "that"?
Well, from my experience, I wouldn't recommend it in answering Duo, which can be very fickle about things like that.
qual è la differenza tra "chi lo crederà?" e "chi ci crederà?", qualcuno sa???
"ci crederà" - believe in us
"Who would believe it"? Or has it another connotation?