A N-14 document is a request for information during the Naturalization interview process. In an ideal Interview, you will be asked questions about your application and background, a few questions to ensure you meet all the eligibility requirements, and if you have an attorney with you, he or she will be asked a few questions. Of course, and additionally, there is the English and Civics test.
Upon completion, you will receive a decision, USCIS will give you a Form N-652 about your interview and will either grant, continue, or deny your naturalization application after your interview.
In the second worst horrid result (the worst being a denial, and the least being an approval) your case will be continued. You will be asked to come back for a second interview or USCIS will provide you a Form N-14. This form will explain what information or document you must provide and how you should return the information to USCIS.
You must follow these instructions, and you must provide accurate information. Failure to do so will result in a denial of your application. If you have an attorney, insist that he look over these documents to ensure its accuracy and its adequateness.