You can find your Send-to-Kindle email address on the Manage Your Content and Devices page on Amazon (you must be signed in). First, navigate to the "Devices" tab using the navigation bar at the top. Then find your Kindle in the devices list, and click on the "Actions" icon to the left of your device name. Your Send-to-Kindle email address will appear in a popup, just above the "Special Offers" link.