Skimmers are primarily a US thing, almost unheard of in the UK and Europe. Why? The data is "skimmed" off the magnetic strip of the card, you cannot "skim" a chip or contactless signal. Further, standard security features in European transactions, such as requiring either contactless, PIN, or 3DS (for online)...so even if a thief collected account data, it is unable to be used. Many cards are even eliminating the magnetic strip, even some US cards have finally announced dropping the strip. They can get rid of the embossed letters as well, just bulk in my wallet. (ATM cards largely have eliminated the emboss). For that matter, many ATMs in Europe are now becoming contactless, just Tap and start your transaction.
Two weeks after back from Paris-Netherlands trip Schwab notified me of a questionable withdrawal on my ATM card. From Mexico, they knew I wasn't there as Schwab still asks you to input the old-fashioned travel alerts.
I hate to inform you, but your card likely was not "skimmed" at an ATM, that just is not how they get your info. Schwab also does not require travel notifications, (have had a card for a couple decades, long ago stopped doing that, for all my cards) and that likely paid no role in detecting fraud. Most likely was the algorithms used in detecting fraud and the lack of card security measures detected. Not sure if that gives you comfort or just makes the worry worse.