Where is the hash key on my surface pro keyboard

take a look at

https://answers.microsoft.com/en-us/windows/forum/windows_10-other_settings/windows-10-keeps-swapping-my-keyboard-layout/17e81e19-baff-4429-86e5-0ab3b087690d

https://answers.microsoft.com/en-us/windows/forum/windows_7-hardware/the-inverted-comma-keys-are-reversed/e204b7aa-933f-44fe-8df9-30a5b0575084

The keyboard is too small to contain all of the keys on a normal keyboard and what you can do is launch the "Character Map" located in Windows Accessories and there, with a pen and piece of paper, located all the characters you want which are not on the keyboard and when you find the character, look at the lower right corner of the panel and you will see a four digit number.  Write that full number down with a sample of your character for reference.

Later, when typing and you want one of those characters, press and hold down the 'ALT' key and type in the four digit number and then release the ALT key.  Your character will be put in place.

You do not change the layout of the keyboard and will have to get used to its particular layout.  Again, the keyboard is just plain too small and only the most used keys are placed on it.  Keyboards can be remapped but tend to loose the setting after a while and snap back to original.