They DO have a reciprocal agreement with Discover, but it may not work on some improperly configured terminals that don't recognise and know how to route the JCB card. At the vast majority of brick-and-morter retailers accepting Discover, it will work. If it doesn't, file a report with Discover - they take acceptance issues very seriously.
This agreement does NOT cover card-not-present transactions, so acceptance on smaller websites is iffy.
Many large retailers do directly accept the JCB card, and will accept it online (like Amazon).
Overall, acceptance will definitely be the lowest of any US-issued major credit card, but it will still be very, very high.
American Express Blue Cash Everyday - $11,000; American Express Platinum Cashback Everyday - £3,000; American Express Rewards Credit Card - £7,500; Aqua Reward Mastercard - £3,500; Bank of America Travel Rewards - $5,000; Barclaycard Freedom Rewards - £3,500; Citi Forward - $5,800; Discover It - $10,000; Halifax Clarity - £1,500; HSBC Platinum with Rewards - $5,000, MBNA Everyday Plus - £3,500
