The overall sentence seems a bit vague. If you substitute a name, the first one sounds good. I did not know Sally knew me. Perhaps the second could be: I was not paying attention to who knew me. But I am wondering 'know' is really the verb you want, and whether 'recognize' may be closer to your meaning.

The first sentence means that you didn't have knowledge of who knew you. The second one means that you were not able to notice which people knew you.

Yes, there's a difference. "to know" is to be certain about something. "to notice" is to perceive, hear or see something.

1 = He had no knowledge of who knew him, and who didn't. 2 = He might have had knowledge of who knew him and who didn't, if he had paid attention to this, but at this time, he did not notice. Perhaps he was too preoccupied by other thoughts to turn his attention to this distinction.

There's a difference in the meaning of the two sentences.