Where to start learning assembly language?

Question

assembler

With ms dos, and then switch to Windows and other operating systems, or just start with Windows?

Answer 1

From the fact that you first need to set a goal: why do you need an assembler.
It's just pointless to teach him.
If you are writing in C/C++, then you will need an assembler for debugging. When you come across this, then teach.
Or you have a strong desire to write your own OS, then you can just learn everything along the way, starting with bootloaders. Here you have to learn a lot, spend at least a couple of years, but the experience gained in writing an OS is a very valuable thing for a developer.
Learning to learn is useless. Better than another skill, learn some.
Nothing depends on the OS, the assembler depends on the processor, its bit depth, architecture.