I think that the closest we have to an explanation for something capable of thinking are CPUs and we're just not sure what the right software is to create independent thought.

This might imply that traits like universal computation are necessary (but not sufficient) for thought.

We can design synthetic chemical painkillers that work, suggesting at for this we actually know what’s going on. You can actually look up how these neurotransmitters etc work.

If you somehow want to suggest something else is going on you really need to support that argument extensively.

Which doesn't explain having an experience of pain, only that certain neurotransmitters are involved which can be suppressed.

I did a bunch of research on pain some years ago, and in order to "standardize" it, one would apply a treatment when the person said pain was greater than 7 out of 10 on a scale.

If pain were measurable "objectively", this wouldn't be necessary.

As to measurement, we can design and build modern CPU’s but can’t inspect them in full speed operation. Similarly, mechanics often need to take something apart to test it. Living organisms present a more complex challenge, but the similarities are obvious.

We have plenty of ways of directly measuring people‘s brains and CPU’s energy use etc. The issue is speed and resolution which is hardly a philosophical limitation.

Different signal sources and also differently configured/trained systems receiving and interpreting those signals.

But practically, it makes more sense to use the instrument already evolved and trained by their own experience to measure their pain: the person themselves.

I think that this is a little too general a statement, given that it could be used to describe almost any human variability.