Not +

Hello, Valent1ne. The first one is poorly constructed and is not grammatical. Second one is good with rectifications as following.

Valent1neI don't know what to do.

Well, the standard phrasing would be:

I don't know what I do.

The other version strikes me as archaic English. I'm not sure if that's exactly what you're looking for.

No, it is an improper use. You can't use Present Simple in that part of the sentence because it sounds like you do something because you don't know what you do. Like you don't have the foggiest idey why is that. And it is nonsense.

"I don't know what I am doing" can fit the bill or "I don't know what I was doing".

Without more context, we can only speculate what is right or wrong.

With context or not, but anyway "I don't know what I do" is not going to be a right thing.

Hi guys,
'I don't know what I do' is OK as a reference to current habits.

eg I don't know what I do, but every day the teacher gets angry with me. Maybe she just doesn't like me.

A famous (and archaic) occu

Thanks Clive. I was quite hasty to jump at conclusions.

When I saw this thread, this Brian Adams song started playing in my head....

It still feels like our first night together
Feels like the first kiss and
It's gettin' better baby
No one can better this
I'm still hold on and you're still the one
The first time our eyes met it's the same feelin' I get
Only feels much stronger and I wanna love ya long

"I know not what course others may take. . . ." is traditional.

My first impulse was to say it's poetic (which it is), but I'll settle for "archaic."

We're still allowed to read old books, but should not use the structure in casual conversation.

I'm quite sure it can be found in contemporary poetry, and I suspect it might find its way into a commencement address.

Thank you for the attention. I did find it in 'bryan adams - please forgive me'  lyrics.

But the point was to find out of 'not + verb'  or 'verb + not' constructions.

Could you share some links to this kind of grammar ...