Which amenity is used for advocate office?
You mean in the main page slippy map ? You can choose between different renderers (Mapnik, osmarender, cyclemap, noname). It is a decision of the rendering styles editors to decide what data is displayed and what is not. The Mapnik map maintainers are usually taking into account popular tags but many are ignored. I don’t know if ‘office’ is displayed or not. You have to try but please don’t replace the appropriate tag but something else just to see it on the map. This is what we call “tagging for the renderers” which is not correct.
Probably the majority of the OSM data are not displayed on the main online map. osmarender is usually showing a little bit more than Mapnik. cyclemap is more oriented to cyclists interest.
Here are some statistics about the key ‘office’ usage in the database:
http://taginfo.openstreetmap.org/keys/office#values
As you can see, although the key is relatively new in OSM, it is quite popular now.