The Unites States Air Force assigns a historian to certain after-action debriefings. The job position even has its own AFSC classification of 3H0X1 where X is a number denoting seniority and certification levels. That job description is readily available as a google search.

The basic idea as explained to me was that a historian asks different questions than the debriefing related to military and operational questions would cover. As the event was very fresh in the minds of the participants, it provided a unique perspective. The historian is responsible also for maintaining documentation for historical purposes. This gets the feedback while it is fresh and there is less chance for the person to generate false memories, or start introducing outside items.

Consider this: There is a story of the surrender at Appomattox Court House that states that General Joshua Chamberlain ordered a salute for the surrendering CSA soldiers. OK. Nice story, but as far as I can tell that the very first mention of this chivalrous act was 30 years later by Chamberlain himself. General Gordon on the CSA side then agreed that this happened. So, is the lack of mention for those 30 years just that the documentation in forms of letters and diaries have not been found, or was this just a story made up later?

Also: Abraham Lincoln went with his secretary to visit General McClellan at his home. McClellan was not there. They decided to wait in his parlor. McClellan came in after a while and immediately went upstairs. They waited for him. Eventually, a servant came and said McClellan had gone to bed and they should come back at another time. The story is often retold, but the first mention of it was when that secretary wrote the definitive biography of Lincoln, which made a lot of money. By that time, the secretary was the only person present who was still alive. Did this actually happen? It could be argued either way. The secretary was certainly very, very biased, but his facts that can be verified by documentation has checked out, even if his interpretation of those events was extremely biased.

So, in answer to your question: Ask historians what interests them, then make it a point to ask those sorts of questions and archive the related documentation so that it is retrievable in the future.