know about someone—
1. have knowledge or information about smb.:
- Knowing what I know about her husband … she is just as delusional as her husband.
2. (negat.) be not sure about a person:
- I don’t know about John, but I was about ready to fall through the floor with shame.
know of someone— = know about someone 1:
- I know of one eminent man of science, who was a burning and shining light in his day.