What assemblies and namespaces should a good .NET programmer know?

Question

ASP.NET

Looking at customer requests, they all require absolute knowledge of the .NET Framework. But there are hundreds of assemblies, thousands of namespaces, even more objects with their methods and properties. Is it really necessary to know all this perfectly? Or maybe it's good enough to know some particular namespaces?
I want to become an expert in .NET web development. But the eyes are wide open. Fear takes. :)

Answer 1

There is a basic set of libraries that will be useful in solving many problems, such as collections, linq, streams, etc.
There are a huge number of libraries needed to solve more specific tasks, such as working with a database, working with a network, encryption, web... the list is very long.
Naturally, it is impossible to know all the libraries from the second list, and most importantly, it is unnecessary.
Accordingly, you need to be able to use general-purpose libraries + specific ones for your subject area. Well, you need to understand how .NET works, what is there at all, then to solve a new task for yourself, you will spend the minimum amount of time, just digging a little in msdn.

Answer 2

You have a misunderstanding of the situation. I don't think anyone would frame the requirement as "know System.Collections.Generic". But if you cannot tell how HashSet<T> differs from List<T>, then this speaks of your experience, which is important for the employer.
Do you want to become a web expert? In this case, to find out the extent of your knowledge, you will most likely be asked questions that require you to be able to work with types from System.Web to answer. But setting yourself the task of "learning System.Web" is not very productive.

Answer 3

usually you look, study and use those that you need)))

Answer 4

Weird question. Who requests? Who cares what you know? The main thing is that the problem is solved.