dog bite personal injury law in GA, procedure for getting doctor's report and other discovery

Your best bet would be to get a subpoena duces tecum issued by the court and to serve it on the doctor (or if they went to a hospital, then on the custodian of records). The doctor or hospital may object, so you must be prepared to show that the records are in someway relevant to your case. I hope you have a lawyer helping you with this. If not, then you should consider getting one.

Although your question is about the criminal trial, your homeowner's insurance would have similar interests in your case. The insurance defense lawyer would not represent you in the criminal matter, but he might have a copy of the doctor's reports.