If you understood how your own consciousness works on a scientific level, you would know exactly what evidence to check for in other people
Leaving aside the difficulties in unpacking the idea of scientific introspection under the classical rubric of experiment as observation, once one decomposes consciousness to where a scientific level can be extracted, there's a corpse on the table not a patient. The whole gist of consciousness is that it's unified and once we admit a distinct 'scientific level' we ought to own up to what we have done and say "by consciousness I don't mean what is ordinarily meant, but instead I mean exactly 'x,y,z' and therefore my claims are not about consciousness in general but about this special definition."
And there's nothing wrong with that, and it might be useful.
To continue with the above thread, wouldn't Wittgenstein's response to this be something along the lines of: if scientifically dissecting consciousness results in a corpse, is it correct to say there was a body in the first place? Think of the question, "How does Helios pull the Sun across the sky?" After dissection, we resolve to question the question, not answer it.
See the "Mary's room" thought experiment. Thinking and reasoning about all the measurable properties of a phenomenon is way different than experiencing them. This doesn't necessarily mean that subjective perceptions have an immaterial existence, but it provides an approach to analyzing the mind that can't be achieved by physical measurement alone.
A better question would be "how can you try to understand consciousness without instrospection?" Studying consciousness merely by performing brain scans and electroencephalograms, without asking the subject what she's experiencing, would surely provide a poor and incomplete perspective.
Leaving aside the difficulties in unpacking the idea of scientific introspection under the classical rubric of experiment as observation, once one decomposes consciousness to where a scientific level can be extracted, there's a corpse on the table not a patient. The whole gist of consciousness is that it's unified and once we admit a distinct 'scientific level' we ought to own up to what we have done and say "by consciousness I don't mean what is ordinarily meant, but instead I mean exactly 'x,y,z' and therefore my claims are not about consciousness in general but about this special definition."
And there's nothing wrong with that, and it might be useful.