which web does the SNAP get the auxiliary data for atmospheric correction?

In processing,much dataset, such as altitude, roughness, zonal wind, meridional wind, atmospheric pressure, ozone, relative humidity, sun spectral flux, can be generated. Which web does the SNAP get the auxiliary data? are they real-time data?

I’m not sure if I understand your question correctly. But If you are talking about Sentinel-3 data (OLCI, SLSTR) then these products contain already the information you have listed.

If you have a look at the OLCI documentation you can see that products are generated in different types. Near Real Time (NRT) and Non-Time Critical (NTC).

The metrological data is retrieved from ECMWF.