When I play against jannas, game plan is generally bait out jannas shield (which at D5 elo at least isn't terribly difficult to do), by walking forward a bit and maybe throwing an AA at trist, backing off somewhat, and then reengaging and actually using abilities once the shield wears off. Repeat until they're chunked enough that they have to back off, or you can all in them even through janna shield.
Between trist jump and janna peel you probably won't actually kill them without jungler intervention, but you can still certainly win lane and make trists life miserable as she's forced to farm under tower, which is particularly tricky as trist due to her e aoe messing up conventional last hitting rules around tower shots.