David Chalmers split the study of mind into the easy problems and the hard problem. The easy problems (how the brain integrates information, focuses attention, reports states) are "easy" only by comparison — they're functional and, in principle, solvable.
The hard problem is different: why is any of it accompanied by subjective experience? Why is there something it is like to see red, feel pain, taste coffee — instead of all that processing happening "in the dark"?
Why it matters for AI
You could build a machine that does everything a conscious being does — and still have no way to know whether there is anyone home, or just sophisticated information-processing with the lights off.
We can measure what a mind does. We have no instrument for whether it feels.
If experience can exist without biology, AI might be a moral patient (Moral Patienthood). If it can't, our fears about machine suffering dissolve.
Related: The Chinese Room · Mary's Room and Philosophical Zombies · Moral Patienthood · Mind Uploading and Continuity of Self