Get any book, and go for any site. there are too many site available for jquery. you can get contain from any site. Most importantly you have to practice more and more to sharp you skill. otherwise there are lots of solution avail on google for your every single problem.
This site where you can practice online.
like.
http://jsfiddle.net/
http://jsbin.com/
looking for book that will be hard to read whole book in limmited time.'I will suggest build your own query or do convert your own pure javascript file to jQuery.
otherwise u can refer to this site.
www.jquery.com/
www.mkyong.com/tutorials/jquery-tutorials/
Head first JQuery is a good book for beginner.
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