In OneNote 2016 the user can email a page in a Notebook using the tab Home - Email Page command.
Where is this command in the Windows 10 OneNote app?
OneNote for Windows 10 is designed like phone App. It can share data with other Apps.
So, to email a OneNote page, click "Share" button on OneNote UWP, in bottom of the "Share" pane, click "Send a Copy" button, it will pop up a window, choose the Windows 10 Email App to send current page as email.