Reading conversations about Attack on Titan I've heard about the anti-Titan artillery, which supposedly is a very powerful weapon against Titan more than the regular cannons. I dont remember seeing it in season 1 and season 2. Have they appeared in the anime? If so, which episode? or this only exist in the manga?
As far as I remember
The anti-titan artillery is developed by other nations (other than Eldians and Marleys) to counter Marleys titans. since we are not introduced to Marleys and the world beyond the walls in the anime, I'd say it's too soon to say there is no anti-titan artillery in the anime.
This was revealed in the manga chapter 91. Season 1 of the anime finished at manga chapter 34. Season 1 had 25 episodes. Season 2 of the anime is said to have only 12 episodes, which means that, probably, season 2 will reach chapter 51 (if the second season follows the same manga-to-anime ratio as the first season).
Never the less, we can say with certainty that the anti-titan artillery will not be revealed in season 2 of the anime.
It is important to keep in mind that when anti-titan artillery was revealed in the manga, it was a huge information, thus it is highly recommended to not engage in Attack On Titan manga discussions when you are not caught up with the manga.