Hi! i need to reset my late wife ipad. the ipad was synced with her personal icloud account and i don't have the password nor access to her mail. What can i do ?

What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

and

http://www.imore.com/how-wipe-all-your-personal-data-ipad-or-iphone

and

http://9to5mac.com/2015/08/25/how-to-safely-prepare-wipe-your-iphone-for-resale- trade-in/

but if you google your question you will find a lot of articles.

Sorry about your loss

If you can bring the original documents of purchase of the iPad along with the death certificate and proof of your identity to an Apple store - they should be able to assist you

Please make a Genius appointment at an Apple Store, or go to another authorized service provider.