[Grammar] "Not that I know of"

[sky3120]

"Not that I know of"

Why do we need of behind? Can we not omit it or can we not put objects behind of or right after know without of?

For example,

"Not that I know."

"Not that I know of it."

"Not that I know the news."
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I think that although "objects can follow know, but "not that I know of" is just an idiom. What do you native English speakers think?

Thank you so much as usual and have a good day.

 

[philo2009]

"Not that I know of" is a fixed idiom and so cannot be modified in the ways that you suggest.

It means simply "not as far as I am aware".

 

[sky3120]

Thank you so much and I agree with you, but I saw this sentence, Not that I know anything about sports. I think that except for the fixed one, this kind of sentence is fine to use. What do you think?

 

[bhaisahab]

Thank you so much and I agree with you, but I saw this sentence, Not that I know anything about sports. I think that except for the fixed one, this kind of sentence is fine to use. What do you think?

It's fine.