In Harry Potter and the Chamber of Secrets, Tom Riddle is interested to know how Harry survived Voldemort's spell. This implies that Tom Riddle from the diary could not deduce/guess what happened that night.
The strange thing is that in Harry Potter and the Goblet of Fire, Voldemort seems to know exactly how the spell backfired (while this process has only taken a few seconds)*. Since Tom Riddle could not guess the cause, it's very unlikely Voldemort could work out this magical challenge himself.
Since the diary was destroyed after Harry's encounter with Tom Riddle, there is no way Voldemort could have learned what Harry told Tom in the chamber. Does this mean both "identities" share a memory and that Voldemort simply has access to the knowledge Tom (from the diary) accumulated at Hogwarts? If not, how did Voldemort work out why the spell backfired?