In a professional context, nobody knows it all in details. There are specializations: core network and RAN, and inside RAN protocol stack vs PHY, and in PHY algos vs implementation, etc.

You can see all the cellular specs (they're public) from there: https://www.3gpp.org/specifications-technologies/specificati...

5G (or NR) is the series 38 at the bottom. Direct access: https://www.3gpp.org/ftp/Specs/archive/38_series

It's a lot ;) But a readable introduction is the 38.300 spec, and the latest edition for the first 5G release (R15, or "f") is this one: https://www.3gpp.org/ftp/Specs/archive/38_series/38.300/3830...

It's about as readable as it can get. The PHY part is pretty awful by comparison. If you have a PHY interest, you'll need to look for technical books as the specs are quite hermetic (but it's not my field either).