Hi Ram, I hope you are asking about XSLT itself. I have learned on the work and from google (searching each use case when it was needed). That is the reason why I wanted to put my learnings in organized way for others to benefit.
There are some online resources like W3 schools etc, but most of the XSLT courses are HTML/WebDevelopment centric. Which was not exactly matching with what I needed for my work (which is data transformation mainly). You can use AI tools like ChtGPT to ask questions as well.
I suggest to start with W3Schools and Udemy etc.. and make use of ChatGPT (or other AI tools) as and when needed.