I thought one in danish could be either En or Et?
It can only be et if one is counting a neuter object (Et, to, tre, fire, fem dyr = One, two, three, four, five animals)
If you aren't counting anything in particular, you can use en or et as you feel like. Most people would accept it even if you are counting something specific.
why wouldn't you use Én instead of En?
èn always means exactly one, where as en may mean one or more, as in "der er en (måske flere) derover" -> "there's one (maybe more) over there".
Just saying that I've repeated this exercise so many times that my brain thinks that "sko" is another word for 'six'.
Apparently duo no longer uses numerals. 1 2 3 4 5 sko.