1. He is taking me to prison.

2. He is taking me to a prison.
3. He is taking me to the prison.
---------------
Are they all grammatical? What is the difference among them in meaning?

4. I'm on duty now, as you know.
5. I'm on duty now, you know.
6. I'm on duty now as you know.
7. I'm on duty now you know.
-------------------------
Which ones are grammatical? Are they all the same in meaning?

1 - 5 are all fine.

1 means taking you to serve your prison sentence.
2 means taking you to some prison somewhere, but it's not clear if it's to visit or serve a sentence.
3 means taking you to the only prison in the area, but it's not clear ...