Su = it is an article, it is telling that the noun is indefinite.
Oficina = it is a noun, it is "office" in English.
Está = it is a verb. It is the Spanish for 'is'.
En el centro de la ciudad = it is a circunstancial complement, it is indication a place
Su oficina = that is subject.
Está en el centro de la ciudad = that is the predicate.
I hope this helps you! If you have more questions, feel free to ask! :)