I have a question about Conway's Game of Life's gameplay, but I can't seem to find an appropiate tag for it.
I was looking for
game-of-life or something similar, but there is none.
What would be the most suited tag for such question?
Just because the tag does not exist, does not mean it is the wrong tag
We create tags on here, as questions are asked in context of the tag. Moderators can create tags, but in the mean time you should get away with listing your 'guessed tag'.
That said, your question is easily off topic, for the purpose of this website. To quote the tour page, designed to give new users an introduction to Arqade,
Arqade is a question and answer site for passionate videogamers on all platforms.
The key word here is video. Game of Life is considered a game, but not a video game. If you could find a video game with the same representation, to which your question would relate to, perhaps it would be considered on topic.
The Game of Life derives from cellular automation, which is studied as a model under several areas. One of them is the study of mathematics. Your question is best asked on Math Stack Exchange.
On this site, you have a cellular-automata tag. This would be one such tag you could use on a Game of Life question.