We hold consciousness to be a marker of "something worthy of ethics" but it's a bit of a species solipsism. Consciousness is a biological process or effect. Why is it more important than other biological processes or effects? Well, because we're humans with "consciousness" and we think so.

To me, consciousness is likely to be explained as an emergent phenomenon allowing humans to collaborate, rather than something that is more akin to the "soul" or "self" that is often ascribed. To my mind, ethics, if we can separate that concept from other emergent phenomena, should be applied more holistically than just to things we believe are conscious.

How does anyone know if their naturally produced neural nets are self aware?

By definition, one can always know their own naturally-produced neural net is self aware (cogito, ergo sum). The open question for solipsists is whether, should someone report to you their neural net is also self-aware, you should believe them.

but how can we be sure that the cogito part is actually happening? this immediately (d)evolves into a purely ontological discussion

Personal experience. We perceive a continuity of experiences, memory, and the difference between that and slumber or becoming insensate, and we call the experience "consciousness" and our knowledge of that "self-awareness." It is definitional; the word descends from the experience, not the other way around.

Perhaps we need to synchronize our definitions of "experience", "perception", "personal", and "knowledge", because your very words are almost exactly what I would say in counter to your point.