"Where are the offices?"
The consonant at the end of офис is not palatalised, and it remains so in the plural.
The major exception are к, г, х, which never have ы following them (even though кы, гы, хы are easily pronounced by native speakers), and ш, ж, ч, щ, which always use an orthographic и over ы (even though ши and жи do sound like шы and жы).
- these restrictions are generally known as "spelling rules" in teaching Russian as a foreign language. But really, they only concern "spelling" with ш, щ, ж, ч, ц, which have a fixed palatalisation. For к, г, and х that's how the word is actually pronounced.
It is a word used with adjectives for certain bureucratic offices («нотариальная контора» ~ notary office) or for a particularly shoddy firm, with a negative connotation. As a result, it is not used as a generic synonym for "office"' similarly how "smartypants" is not a generic synonym for "person".