I can't speak for everyone here, but the "knowledge about stuff" is something I add to my characters. They are born with little to no knowledge, and they learn as they go and interact with the rest of the characters, especially the craftsmen or any person specialized in a particular subject.
I can understand if a character figures out on his/her own that he/she can sharpen a flint to make a stone cleaver, make a bone knife or even collect some logs and build a raft without seeing somebody else doing it, but not more complex tasks like making jewellery (Unless it's made of bone), refining steel and making weapons, or building a raker from scratch without even seeing one (Even if I had access to all the required materials and tools).
Of course, as a character starts progressing on a specifical path, I can understand if he/she figures out more complex things. As a hypotetical example, I have a character who likes cooking, and he discovers that he can grind wheat in order to make flour and cook bread. If I get my hands into some sorghum, I'd (As a character, of course) think "Hey, maybe I can try grinding these grains and make bread out of this, just like wheat". But a character who has some kind of "revelation" and suddenly knows how to make bread without at least seeing or being told about the process sounds a bit like a scene from The Matrix:
Neo: "Can you fly this helicopter?"
Trinity: "Not yet. Morpheus, I need information on how to fly a blahblah chopper..."
(Morpheus uploads the info)
Trinity: "Now I can, let's go"
And now for a real example, one of my (old) characters left his hometown to wander the roads at a very young age, and while he was there he learned pretty much nothing. While travelling, he arrived to a desolated town, and found a half-made fur undershirt made of furs stitched with sinew. Besides discovering that he could complete the fur shirt (He had the materials), he reverse-engineered the concept and made a pair of trousers, mocassins and a hat with the same materials and methods. Another example could be the making of a shield. He had seen the shields and why people used them but never made one, so he used bones to make a imitation of an animal ribcage, which he had seen when skinning the animals he hunted.
In essence, there's no need for a system like that, the only need is some common sense when you roleplay (In my opinion at least

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