The Doctor's office (The Pilot)

By the 2010s, the Twelfth Doctor had his own office at St Luke's University.

He kept many of his belongings in his office, such as a cup containing his old sonic screwdrivers, portraits of River Song and Susan Foreman, busts of Ludwig van Beethoven and William Shakespeare, and his TARDIS parked in the corner of the room with an "out of order" sign hanging on it.

Nardole once took Bill Potts there, where the Doctor asked her why she went to his lectures if she wasn't a student of the university.

Bill asked the Doctor how he brought the TARDIS into the office, noting that it would be impossible to move it in if he didn't need to assemble it. The Doctor explained that he had the windows and wall removed to have a crane lift it in, but Bill later noticed the TARDIS parked on top of the rug she had given him for Christmas. Bill later fled here when prised by sentient oil, the Doctor and her fleeing in the safety of his TARDIS. (TV: The Pilot)

On one occasion the Doctor sent Nardole to put the kettle on in his office while both he and Bill secretly had an adventure on a human colony planet. (TV: Smile) Returning to his office after the following an unexpected detour to London 1814, the Doctor and Bill found Nardole bringing tea "with a bit of coffee". Nardole was dismayed to discover that the Doctor had neglected his promise while the Doctor argued that his return was evidence that he had kept it. (TV: Thin Ice)

Following his adventure at Chasm Forge, the Doctor was at his desk as Nardole chastised him for once again abandoning the vault before he stood up and declared he was blind. (TV: Oxygen) The Doctor later attempted to return to his office but was wary of crossing paths with the Monks, opting to go to the vault instead. (TV: The Lie of the Land)

A virtual version of the Twelfth Doctor in a shadow world held a meeting with the Pope here when learning of the Veritas. (TV: Extremis)

Behind the scenes
According to the Doctor Who The Official Annual 2018, which is not accepted as a valid source for in-universe articles on this wiki, the Doctor had asked for his office to be on the first floor of the university building, both in case of a Dalek attack and because he enjoyed the exercise. He would also dismiss his TARDIS as the place he stored umbrellas in.