Accessible through the Arboretum, Alex's Office contains a safe with a randomly generated safe code. This means the code is different for everyone in every Prey playthrough. However, how to find the safe code is the same every time.
The safe code for Alex's Office Safe can be found by searching the remains of December, shortly after being killed by January. You'll have to listen to December and backtrack through the Neuromod Division.
Prey (2017) Alex's Office Safe Code - GameRevolutionWATCH GALLERY