Southern Italy on Adriatic coast

Just consult a different book--RS does not cover all regions exhaustively. The area is well covered on the internet as well.
Give us more info: Do you want to be right on the sea? Town/city/village? Type of transport? How are you arriving/departing--from where?
I liked Monopoli, a walled fishing town. I bypassed Otranto, but that would make a fine choice if you want right on the sea. I adore Lecce, which is close to the sea.

Thanks for your reply!
We are doing his Southern Italy tour , ending in Naples and we have 2 days and nights before returning to Rome to depart.
Being on or near the sea is my preference, small, quaint , good walking…and not to difficult to get to and from, as we will not have a car.

I would compare the train times from various spots since time is tight. Bari will be your departure point back to Rome so I would stick close to there, and Monopoli and neighboring Polignano a Mare are just a short train hop from Bari. Bus from Naples to Bari might be your better option than train but not sure.
Will you have really explored the Naples and Amalfi Coast area exhaustively? If so, there are some nice towns just to the south of Salerno (the area is called Cilento), and that might make better use of your time. I'd look at Maratea also since the train goes there. good luck!

It’s not on the Adriatic, but Sperlonga and Gaeta are beautiful and between Naples and Rome.

Another vote for Sperlonga. Nice stop from Naples if you are headed to Rome. https://theculturetrip.com/europe/italy/articles/romes-8-best-beaches-accessible-by-public-transport/

I thought of Gaeta too, but was not sure of the transport. Maybe check flixbus?
kj: Are you building in enough time in Rome before your flight? If it is morning, I'd be in Rome the night before. If it is afternoon, you have more leeway, but things like train strikes can happen--as we are seeing lately.
I am thinking more that if you don't want to stay anywhere on the Amalfi Coast (Cetara was great), one of the towns near Salerno might make better use of limited time. I have only stayed in Pisciotta, which is up on the hillside, but I have heard great things about Santa Maria di Castellabate. If you won't get a chance to see Paestum on your tour, it really is a sight to behold. I can't say I'd make the trek to the Adriatic with only two days.

We spent ten days in Polignano a Mare on the Adriatic in Puglia. Beautiful place!! Hotel Covo dei Saraceni.