I joined kdp middle of last year, and recently received my 1042-s form . I am a non US self publisher and wondered if I need to do anything with this information? Amazon withholds 30% taxes already. I'm assuming they send this on, on my behalf?
Where are you located? If you're in the UK, you don't actually have to pay any US taxes if you've filed the proper paperwork. If you're in Australia, you are required to pay 5% in taxes, not 30%, again if you've filed the proper paperwork.
There are many thread in the Account forum (the first one) on getting an EIN (the number you need), filing the W8-BEN form to stop tax withholding, and finally filing the 1040-NR form to get back taxes that were withheld. Good luck!
For an EIN, call 001 267 941 1099 -- a dedicated department in Philadelphia for foreign entities getting an EIN. Unlike the UK office or the IRS head office they'll actually know what you're talking about when you ring. (Five-hour time difference, so call in your afternoon or early evening.)
Some have reported that the IRS doesn't want to issue EINs any longer for this purpose, but you never know.