I researched this as we are moving offices (in Israel - but for a global 'non-Jewish' corporation).
The practical halacha is that one places a mezuza in an office but without a blessing. Since an office is not a permanent dwelling in the same was as a house, there is a doubt if it absolutely requires one. On the other hand, since in our times, people spend significant periods of time in offices and eat there, it has certain characteristics of a dwelling. Thus the mezuza but without the blessing.
Specifically to be obligated in mezuza, a house needs to be a dwelling place - an office doesn't fully qualify (Mishne Torah, Hilchot Mezuza, 6:1, SA YD 286:11 speaking of a store, see also Shulchan Haruch Harav here and here)
Note an office where one sleeps might have a different law. CYLOR.
Addendum: I saw now that R Eliezer Melamed rules that one may say a blessing in a store or office if one eats there (Peninei Halacha Likutim vol. 1, Mezuza ch. 6)
It seems that if the sellers are accustomed to eat there over the
course of the day, one may recite a beracha upon affixing the