Are Euros accepted in Gothenburg or is conversion to Krona possible?

You won't be able to withdraw Euros easily. There could be a limited number of special-purpose ATM in larger banks but I have personally never seen one in Sweden and/or Denmark (I have seen some in Switzerland). Regular ATM won't offer Euros.

What you should be able to do is withdraw Swedish Krona with your Euro-denominated card (or perhaps even directly use your card in shops). Obviously, someone (card-issuer or ATM operator) is going to charge you for the pleasure, in the form of an explicit fee or a buy-sell spread compared to the current exchange rate but that might still be better than changing a lot of cash in advance and carrying it around.

You could also come with some Euros you bought elsewhere and some businesses will probably accept them but buying foreign cash at home and then changing it once more or spending it at an unfavorable exchange rate is very unlikely to be cheaper than using your card.

Although many businesses in Göteborg accept Euros in cash, the most convenient option is just to use your card for everything. Parts of the transport system don't accept cash anyway. It doesn't matter what currency your card holds; it will be converted to SEK when you make a transaction.

Important to bear in mind: Although some businesses (mostly in hospitality) still allow you to sign receipts instead of using your PIN, they do not check for a signature on the reverse of your card and may instead ask to see photo identification, which will need to be a passport or driving license.

Swedish stores have no obligation to accept Euro or any other currency besides Swedish krona. The exchange rate at the stores/chains that accepts Euro is far from the best for you as a customer.

Your probably best option is to withdraw local currency/pay directly with card (I see other answers already touched upon that). If you want to exchange some cash at a currency-exchange-office there are several locations in Gothenburg, split between Forex and X-change but the fee for exchanging to krona (without a receipt) is a bit high for making several exchanges.

Lastly a bit of advice regarding the public transport system in Gothenburg: Västtrafik (http://www.vasttrafik.se/#!/en/). The systems used to pay the fare is not optimised for visitors: there is no way to pay the driver directly (unless you travel far out from Gothenburg), there is no ticket vending machines at stations, only some vehicles offer ticket vending machines, and to pay via sms you have to pre-register at the website mentioned. So I would recommend either register in advance so you can pay via sms or purchasing a suitable ticket-card from any shop that carries them (marked with the logo) before your first travel in Gothenburg.