I also tried melee for about 15 minutes and it wouldn't pop, first musket shot on the Annoying Jellyfish quest (https://bdocodex.com/kr/quest/3530/1/) from Merio using the Practice Matchlock and I got it.
1
Anonymous 18-09-2017 19:36
Для получения знания арендуйте Ружье для тренировки и убивайте мобов им. Ближайший НПС для аренды Мерио.
I had the knowledge and I deleted it with the Elixir of Oblivion and now I can't get it back even with the rented pistol from Merio. Can anyone else confirm this? Same goes for Water Strider.
To upgrade this knowledge to S did not have to delete it with the new knowledge system, but a hunting Matchlock didn't work only the Practice Matchlock that I rented from Merio