Knowing that one knows. Its root is not solitary awareness but KNOWING WITH - the Latin says two parties share what is known.
Latin conscius (knowing with, aware), from com- (together) + scire (to know), with the abstract suffix -ness; knowing that one knows, rooted in a shared rather than solitary awareness.
Knowing that one knows. Its own root refuses solitude: to be conscious was first to know something alongside another, and that shared sense never fully leaves the word.