Just saw the edit so here's my fo reals answer:
Even if you knew what area of speciality they're into, it's hard to get them something DS relevant that they don't already have.
I would say this XKCD book which I think lots of DS would be into: https://www.amazon.com/How-Absurd-Scientific-Real-World-Problems/dp/0525537090/ref=pd_lpo_1?pd_rd_i=0525537090&psc=1
There’s actually a book that covers the exact topic that you’re discussing https://www.amazon.ca/How-Absurd-Scientific-Real-World-Problems/dp/0525537090
Hope your recovery goes smoothly the next few weeks!
You should try reading "How To" Absurd Scientific Advice for Common Real World Problems".
It is hilarious but also goes into some nifty engineering explanations. The writer includes some fun comics. I borrowed it from the library a while back and really enjoyed it.
The book that I'm most interested in now is Sewer, Gas and Electric: The Public Works Trilogy a friend described it as "if Futurama writers made a book".
Treat Yo Self