How do I get the coordinates in the Windows 10 edition of minecraft?

Firstly, F3 is the default to bring up the debug screen. You can change this by opening the pause menu, then choose "Options", then "Controls". In this list look for the "Debug Screen" option, and it will show you what it is currently set to.

The only thing is that some keyboards (primarily on laptops) require you to use Fn or Alt with the F3, due to the keys having multiple functions (like changing the volume, or screen brightness, etc.).

The alternative is to use a command:

/tp ~ ~ ~

Which teleports you to your current location, And will show your coordinates in the chat like:

Teleported Player to 0 0 0