Hello,
Is it possible to get values of what users are restricted to view certain item columns via the API?
Are you looking for the info which users are restricted to which columns? That is not possible through the API.
Or are you looking for the content in a restricted column? In that case it depends "who is asking… 
). An API call is always made with the credentials of a user. So, it depends if taht user (who’s credentials / token) are used have access to the column.