As stated here, Episode 24 of the 2nd season of One Punch Man is based on Chapters 83-84 (Volume 16) of the manga. If you want to pick up where the anime ended, either you start reading on these chapters or proceed to the one that follows, which is Chapter 85.
Which chapter of the manga does Season 2 of One Punch Man anime end in?
Where can I read the original One Punch Man - Anime & Manga Stack Exchange
If you want to keep following One Punch Man story in the manga, after the third season of the anime ended, you need to know which chapter of the manga the anime ends.
Which chapter of the manga does Season 3 of One Punch Man anime end in?
3 Mosquito girl was one of the first monsters we saw Saitama apparently killed. Later in the manga, she reappears. How did she survive that Saitama punch which apparently completely smashed her, and converted her in a large splash of blood over a building?
one punch man - How did Mosquito girl survive? - Anime & Manga Stack ...
Which one is the original One Punch Man, the webcomic or the manga?
Which version of One Punch Man is more expanded, the webcomic or the manga?
As you said, the last episode of the second season of One Punch Man is based on Chapters 83-84 of the manga. With that information, you can easily Google to check the OPM Wikia: The webcomic chapter is #54. The Wikia shows you which episode is based on which manga chapter and webcomic chapter. You can also use this site to check for the details in a different order too.