Aside from palaver, disputation, debate and perhaps dialectic, many of the previous suggestions have addressed the kind of talk that would go on within the “friendly verbal duel”. This is true of spar, banter, repartee, badinage, all of which are forms of humorous, witty, or argumentative talk. These latter four forms of talk could go on within such a duel, but do not in any way describe its overall form.
In addition to palaver, debate, etc., words like the following may be appropriate:
• symposium, “A conference or other meeting for discussion of a topic, especially one in which the participants make presentations” — en.wiktionary [An additional definition of symposium" may be relevant: “(in ancient Greece) A drinking party, especially one with intellectual discussion”.]
• conference, “An event organized ... to discuss a pressing issue ...” — en.wiktionary
• forum, “A gathering for the purpose of discussion” and
“A form of discussion involving a panel of presenters and often participation by members of the audience” — en.wiktionary
• panel discussion, “A conversation about a specific topic conducted by a group of experts, usually either in the presence of an audience or in a broadcast ” — en.wiktionary
• roundtable, “A conference at which participants of similar status discuss and exchange views” — en.wiktionary
• seminar, “A meeting held for the exchange of useful information...” — en.wiktionary