Is it possible to access the F-Keys using Windows Touch Keyboard,
I'm using Windows 10.
Yes. Full instructions below:
The Windows 10 keyboard was originally designed for touch users on tablets, so by default the keyboard is kept to a limited set of keys than you'd find in a regular PC. This allows Microsoft to make the keyboard bigger and easier to tap the keys, but at the cost of some missing functionality -- like the Function (Fn) Keys and number keys row, and the ALT key.
To switch to full keyboard layout, you have to turn the options on in Windows Settings.
Open Windows 10 Settings from the Start menu.
Click or Tap on "Devices".
Click or Tap on "Typing".
Toggle "on" the setting for Add the standard keyboard layout as a touch keyboard option.
Click or Tap the keyboard icon in the task bar.
(If you don't see the icon, right-click or long-press on the taskbar and select "Show touch keyboard button.")
Click or tap the keyboard button at the bottom right of the on-screen keyboard.
Select the standard keyboard icon. It's the right-most icon.
Now you'll have access to the ALT, Function, Tab and other keys missing from the default touch keyboard. To switch back, head to that keyboard button again to change the layout.