Great, I love discussing this issue with you. It's like the cavernous pit that Kirk's security man falls into....There's no hope of resolving this question, Captain, it's bottomless...
I believe that there is a sensible way to prove consciousness. If a freshly made android (computer in humanoid shaped body) could develop self interests beyond the basics (more than just survival and prosperity) and empathy/compassion for sentient beings without having beneficial dependencies to itself, all self learned (without any programming assistance), I'd feel safe in calling it sentient. We actually run on a biologically formed program that was initially written by our genetic coding and then has been continually augmented from the moment of birth up through every living day. We are directly taught some things, but a majority of what we learn is all about self interpretation of incoming stimulus.
Dr. Korby was sentient. But I believe he discovered that he had lost some of his essence. He became aware that his "soul" hadn't carried over, making him a mere copy. His consciousness was mostly copied, but not completely transferred. That's my take on it... I'm not saying it's fact, because the episode is too ambiguous for a definitive answer.