1>> Is this technology is in demand or not in market?
2>> If i want to learn this then what should i do?..i have heard about a book “Agile Web Development with Rails”. As the name tells us that this is for development. but is this book can be used for learning web designing in Ruby?
Rails is a web development framework (with the emphasis on development).
If you are interested in designing websites using SASS and LESS, why not do just that?
You can do so completely independently of Rails.
Here are a couple of tutorials to get you started:
SASS and LESS are definitely good tools to have in your arsenal (although I don’t think you’d need to learn both), but I’m not sure how much knowing them will help you get a job.
I do some work as a freelance web developer and do some work with LESS, yet none of my clients could appreciate the difference between LESS or CSS (although to be fair I’ve never explained it to them).
If you’re going for jobs at web design agencies, maybe it’ll count more then.
The more important part of the puzzle is that if you would like to work in a ruby environment familiar with ruby and rails. That is probably 1000 times more significant than experience with LESS or SASS. That is really the same with any server-side technology whether it be php, python, .net, etc. Candidate familiarity working with a companies chosen programming ecosystem will be a significant concern for the employeer. While something like LESS or SASS might be part of that ecosystem those really aren’t core components unlike a server-side language. If you are interested in Ruby than learn ruby and rails than maybe a CSS pre-processor.