I am applying for a training-based Schengen visa. I have to go to Germany and work on a research project with a prof. for about 6–8 weeks. The prof. is providing me the accommodation at his home, a small isolated room. The visa requires, "Proof of Accommodation", a "Training Approval letter", and a "Covering letter". I wanted to know the exact format for these letters as per what the embassy looks for
You need to contact the embassy to get either the template or instructions concerning the details of the letter. As it has already been suggested, there is no single format for such letters and it is up to the embassy to decide what types of letters are accepted. Good luck.