Davidson's is a grocery store in Texas.
In Season 4 Ep 17, (A Black Hole), President Hagemeyer calls Dr. Sturgis to offer him his job back, but John reveals he's now working as a bag boy at Davidson's grocery store, while Mary Cooper was shopping here and she walked up to the counter where Madge was working the cashier. She was surprised to see John Sturgis working there. She was told he got a new job after he quit.
In Season 5 Ep 3, (Potential Energy and Hooch on a Park Bench) Sheldon is talking to John Sturgis here. He mentions that despite John having a PhD, he is wasting his energy working as a clerk at Davidson's store. Sheldon tries to convince him to return to the university.
In Season 5 Ep. 6 (Money Laundering and a Cascade of Hormones) , Sheldon goes here to seek advice from John Sturgis, who tells him it's inappropriate to ask random people about sexuality. John is fired by the manager for this, who also tells Sheldon that such questions are not appropriate.
Additionally, in Season 7 Ep. 8 (An Ankle Monitor and a Big Plastic Crap House) Georgie got hired there only to quit immediately after Jim offered a job as a salesman at his tire store.