in Ganga when the job has completed do:

jobs(jobnumber).subjobs(subjobnumber).backend.getOutputDataLFNs().getReplicas()

that gives you a logical filename (LFN) in the first part:

{'/lhcb/user/a/abuechle/7164/7164556/minbiasMC09_35TeV_25Jan10.root': {'CERN-USER': 'srm://srm-lhcb.cern.ch/castor/cern.ch/grid/lhcb/user/a/abuechle/7164/7164556/minbiasMC09_35TeV_25Jan10.root'}}

The LFN is then '/lhcb/user/a/abuechle/7164/7164556/minbiasMC09_35TeV_25Jan10.root'.
The data will end up in the SE closest to the location where your job did run.
The command also tells you on which SE your file is in the second part. So the file is on CASTOR at at the srm address: srm://srm-lhcb.cern.ch/castor/cern.ch/grid/lhcb/user/a/abuechle/7164/7164556/minbiasMC09_35TeV_25Jan10.root.

If you want to know the status of the SE on PIC for example do the following on lxplus:

SetupProject Dirac
dirac-dms-show-se-status | grep PIC