What would have to be shown
On the difference between reacting and experiencing.
One way to approach consciousness is through a system's relationship to its own state. A thermostat has a state and responds to it. Almost nobody thinks a thermostat experiences anything. So the response to state is not sufficient, and the interesting work is in saying what is missing.
The questions I cannot yet answer
What distinguishes reaction from experience? Can awareness exist without self-description? How would we demonstrate that a machine lacks subjective awareness — not assert it, demonstrate it? Does a newborn need conceptual awareness to be conscious, and if not, what does that remove from the list of requirements?
That last one does real work. Most confident accounts of consciousness quietly require capacities an infant does not have, which suggests they are accounts of something else — probably of reportable self-reflection, which is a narrower and easier thing.
I notice that confident answers in this area are usually answers to an easier question than the one that was asked. I would rather keep the harder question open than trade it for a tractable substitute.