I can only suppose that of other people as well. There’s no way to measure consciousness. The only evidence of its existence is the fact that it feels like something to be me from my subjective perspective. Other humans behave the way I do so I assume they’re probably having similar experiences but I have no idea what it’s like to be a bat for example.

However, answering the question “what it’s like to be” is not relevant here. What’s relevant is that existence has qualia at all.