Hello, I was wondering what the powers of a knight of life would be, for example, would he be able to make plants grow or things like that.
The Knight class is the main warrior class! You exploit your aspect as a weapon, which makes it an ACTIVE class. You use your aspect in every possible way you can to protect your team, exploiting it however you can and whenever you can. Quite cunning. Example: Dave, Karkat, Latula
The Life aspect is all about life (literally). As a Life player, you grow, and grow, and grow in order to overcome the obstacles in your life, most likely with a healthy dose of optimism. It ties in with the aspect of Doom and it's figurative meaning is growth. Example: Jane, as the Maid of Life, "creates" (bakes) "life" (energy sustaining food... like cake).
As the Knight of Life, you use living organisms around you (and perhaps imbue life into surrounding objects) in whatever way you can in order to reach your goals. Though at risk of burning yourself out (using up all that life), you use your growth throughout the session in creative ways.