Well, this might seem a very generalized response, but their fellow conversation topics would likely be whatever they might agree on or share in common. This is usually the little things, every-day actions and stuff like that. It's been observed in many conflicts in RL, whenever there is a pause in the conflict and opposing forces manage to meet peacefully. WWI, Korean war and likely others I can't think of atm.
Note though that cases like this involved mostly type 1 enemies; it's hard to do anything other than fight when your facing a type 2 enemy after all.
As for EVE examples, well, Amarr VS Minmatar strike me as mostly type 2 - many Amarr consider the Matari sub-human and godless, while many Matari consider all Amarr to be evil and despicable to the core. In the back-drop for this you find some of the other option, but to get a civil, non-agressive convo going between them you have to find a Minmatar that looks beyond the Empire's policy and religion, and an Amarr who are somewhat tolerant and open-minded regarding his 'godless' opponent.
Gallente VS Caldari is likely a bit more type 1 than 2, if only due to their conflict being younger, not quite to hot, and partially political, partially ideological, partially nationalistic, ass opposed to ENLIGHTEN THE HEATHEN TERRORISTS/FREE THE SLAVES AND KILL THE SLAVERS kind of conflict. But then you have Damar/Kim grade vitrol and such, so again, you will need cool and collected heads who bother with conversing up the enemy.
Keep in mind also that being a capsuleer gives one a rather unique outlook on things, if the toon you play learn anything from the ordeal of becoming one and seeing things from new angles, as well as the old. I imagine a conversation between two capsuleers of opposing nationality in a war would be different than two baseliners doing the same.
Topics could be whatever you do in a civil life. Food, sports, architectural design in various different societies and groups, clothing styles in the same, music, social mores, the fundamental differences the two parties have in all the above-mentioned categories, what they have in common, personal opinions on any of these things.
Finally, minor point; I find it funny how capsuleers find it in themselves - likely mostly due to player desire to see these places - to seek out and join bars and parties and social gatherings of supposed enemies, in the first place. From a realism stand-point, one would assume the moment you show up you get your head blown off, unless you intend to do just that to the attending patrons. Perhaps more likely with type 2 entity. "This guy, part of (insert group) whom I hate due to (insert reason) is having this party with all his friends, family and associated attending. Should likely go visit, introduce my old 557".
Well, again, capsuleers are a bit beside the baseliner standard. The enemy of today might be the friend of the next decade. Though this also holds true for baseliners. It costs nothing to be civil about it...