where do i find?
If you just want some pieces of Light Leather, you can easily buy them at the Auction House, which you will find in the Trade Distict in Stotmwind ( and many other places).
If you are a Skinner, and want to get some Light Leather by skinning kills, this page has a list, with maps and routes
https://www.wow-professions.com/farming/light-leather-farming
most of the Light leather comes from skinning lower zones such as anything around Elwynn, Westfall, redridge or sometimes Duskwood. it also depends on your level if you are able to get scraps or leather (scraps x3 you can turn into x1 light leather) but once you hit a certain Gathering level they might start to turn into Medium leather. (not sure if this changed do to Toon scaling or not… but My past experience is you can skin all the way up to stranglethorn for light medium and sometimes heavy leather. Good luck!