it is easy to compute the PDF (partial radial distribution function) function for different system components and there is different ways to do that in lammps.
you can just use this command
compute rdfagag all rdf 200 1 1
compute rdfcago all rdf 200 1 2
compute rdfcagh all rdf 200 1 3
i supposed here that Ag atoms are type 1, Oxygen atoms are type 2, and Hydrogen atoms are 3.
you can find more information by reading the lammps manual.