Upvote:1
Do I have to go to the German consulate (for me Atlanta) since it will be my only destination country in Europe?
Yes.
Do I apply for a fresh Schengen visa or ask for an extension of the visa (if such a process exists) depending on my date of appointment being before or after the 8th of July?
There is no extension process. You will apply for a new visa.
If I need an extension, do I have to go to the Italian consulate I went to or to the German consulate?
You do not need to do anything with the Italian consulate.
It may be possible that you do not have to go to the German consulate in person because your biometrics will be on file.