I believe we can study consciousness scientifically, even if our observations are limited to asking people what they experience, and making the grand assumption that the person is conscious (not a philosophical zombie). But the science may be limited by what is technologically possible.
As for something that may not be accessible to scientific endeavour: qualia. How can you know that what I perceive as the color red is the same as what you perceive as the color red? Maybe my red is your blue. Maybe my red is unlike anything you've ever experienced. How can we possibly know?