If you are required to send your letter of recommendation to a specific person (may be your future advisor), the admission committee, head of department or an office in the university where you are applying to, then you should tell your professor to address that specific person or office. If in the guidelines of your application, you have not seen any emphasis on to whom/where should the letter be written, then ask your professor to write you a general recommendation like the one indicated in the @Srikanth's answer.
P.S: As I read the first paragraph of your question; I think your professors want to know what is most important for you to be included in your letter of recommendation. Something which will positively affect your application chance and something that should become bold in their recommendation. Of course they have many students in their classes and they may miss some positive and important points about you. So, they ask you to remind them the important things which comes to your mind. I have seen some professors that ask the students who want letters of recommendation to write a draft themselves and by reading the draft, they write a recommendation letter for their student.