Topic: Buying a switch game to other person

I'm from Europe, I want to buy a switch eshop card to a friend of mine from US so they could buy either splatoon+DLC or the Octo:Expasión alone, depends on the situation.
Can I buy them a card from EUROPE and then send her the code of said card? and if so, can they register it if they switch their console from US to EUROPE?

They can create a EU or UK nintendo account and use that for eShop from UK or EU. What is it that they have to buy oversea eShop?

I believe eShops are region locked for eshop codes. What you can do is go on Amazon US and buy a code there. Amazon will send you a code which they can use. I am not aware if Amazon US accepts EU credit cards though.

They do