In the EU, the Payment Services Directive 2, article 3(o), which went into force in January 2018, requires that ATMs inform you of every fee and charge added by the ATM operator before you make the withdrawal.
As Aganju says, free-standing ATMs are generally more likely to charge additional fees than ATMs at bank branches.
Usually the withdrawn amount will be reported in the currency you actually get and your card issuer will convert it to your currency according to their own rules. Card issuers often add various fees to out-of-country cash withdrawals, but that is independent of the ATM being in Europe specifically. Familiarize yourself with your card issuer's conditions before traveling. If you have multiple cards, it is possible that the one that is cheapest to use at home is not the one that is cheapest to use abroad. (And this may differ between use in stores and ATMs).
Some ATMs offer to do the currency conversion for you and charge your card in your own currency. This uses exchange rates set by the ATM operators. The rates will usually be worse than what your card issuer would use. The Directive requires that the ATM must show the exchange rate (and any other fees connected with this feature) before you choose to use it. Unfortunately it's not easy to check your issuer's current rates while you're standing at the ATM, but if you remember their latest published rates you will at least have a fighting chance of judging whether you're being offered a bargain or a scam.
Unless you hit a particularly greedy ATM operator, withdrawing local currency at an ATM will almost always be cheaper than exchanging cash from home. Getting physical euro notes transported to your home country just so you can carry them back to Europe costs money, and those costs will be borne by you in the form of worse exchange rates than electronic transactions carry.