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?
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.