This is the 12340th most frequent Russian word.
каком
"Каким" means "which" or "what kind" in English (instrumental case of "какой").
The word "каком" is used here to ask about the particular city someone resides in, serving as a question word indicating a selection or specific type.
В каком городе вы живёте?
In which city do you live?
In this sentence, "каком" is utilized to inquire indirectly about the specific building of interest, reflecting curiosity or consideration.
Я думал о том, в каком она здании работает.
I was thinking about which building she works in.
Here, "каком" functions as part of a discussion regarding the advantages of different kinds of transportation options, highlighting distinctions or preferences.