You have likely seen some of those channels on Youtube like Primitive Technology, Jas. Townsend and Son, Inc., Survival Lilly or Marcin Jakubowski, who recreate ancient technologies, gadgets, food, or culture, rediscovering the way something was done in the recent or ancient past.
They are doing it not because it is necessary to build ancient huts, furnaces, or pies, but because they enjoy the role of pretending that they are in some other time, experiencing how it was back then, being someone “else” in those circumstances.
Sometimes, we do it for the sake of archaeology, just trying to recreate the process because it was lost or forgotten a long time ago.
One day, I can envisage, we will all have that knowledge as part of us, without the need to learn it. It will be uploaded in our brains, becoming part of our neural networks. Maybe everyone will not know everything knowledge wise, but it is likely that the most important knowledge will be categorised and spread across the population, according to each person’s own affinity to particular fields of knowledge. All that will depend on the capacity of the neurolace and our gray mass to serve as civilisation’s storage.
Apart from becoming a multi-planet and multi-solar species, learning all those terabytes of knowledge will be essential, and we will do it as a safety backup — just in case if some major catastrophe happens. This learning process will be effortless, so there is no need to fear that we will need to spend majority of our life over endless stream of books or virtual pages. It will be done either through DNA engineering or artificial nanobots that will improve our natural abilities — and maybe even help us to upload our brains into some future computer memory.
In that way, we will preserve civilisation, so that, in case of a catastrophe, we won’t need to start again from scratch — of course, that is if the catastrophe is not so large that it will wipe out part of our habitable universe.
So, the job of rebuilders would be to recreate civilisation from scratch, with fewer technologies at our disposal and in the shortest time possible — a much faster than it was necessary to invent those things or create them during standard economic development.
We will do it as a hobby; we will do it as a sport, just for the sake of engaging our mental and motor skills and our personal enjoyment.