Here I would like to ask whether it is worth doing ETN mining at all, given the fact that such difficulties arise with its exchange and application?
Since you are a beginner; For future reference, the first and best way to know where a coin is trading on is by going through coinmarketcap, then using the search engine to search for the coin or token you want, samething can be done for exchanges so that you don't visit a phishing website. So after getting the search result, you can proceed to the exchange to sell or buy as the case maybe. Talking about ETN it is listed on several cryptocurrency exchanges already of which I find Kucoin better owing to volume, trading pairs (that is, you can sell to BTC, USDT or ETH) etc, and as for those exchanges you mentioned, I do not think ETN is trading there; so you can visit coinmarketcap and do the needful. Furthermore, you asked about their mining, I don't know much about it now because when I tried then, it was a waste of time.
For Coinmarketcap visit: https://coinmarketcap.com/currencies/electroneum/markets/