Where do you find the format to use for medical transcription when transcribing for doctors?

Formats for medical reports are pretty prescribed (no pun intended). A good start is to look in the AAMT Book of Style put out by AHDI. Another place is a book called Medical Transcription Guide: Do's and Don'ts. Most people learn proper report formatting through a quality MT program. You can't just "do" MT w/o quality training. All medical facilities have their own formatting styles. The most common formatting for doctor's office notes is SOAP (subjective, objective, assessment and plan). This is what I would use if they don't give you a specific format.