Here is an example using pg_depend, a postgres catalog:

select 
        classid::regclass         as  "depender object class"
   ,
        case classid
        when 'pg_class'::regclass then objid::regclass::text
        when 'pg_type'::regclass  then objid::regtype::text
        when 'pg_proc'::regclass  then objid::regprocedure::text
        else objid::text 
        end
            as "depender object identity"
    ,
        objsubid
    ,
        refclassid::regclass as "referenced object class"
    ,
        case refclassid
        when 'pg_class'::regclass then refobjid::regclass::text
        when 'pg_type'::regclass  then refobjid::regtype::text
        when 'pg_proc'::regclass  then refobjid::regprocedure::text
        else refobjid::text
        end
            as "referenced object identity"
    ,
        refobjsubid
    ,
        case deptype
        when 'p' then 'pinned'
        when 'i' then 'internal'
        when 'a' then 'automatic'
        when 'n' then 'normal'
        end
            as "dependency type"

from pg_catalog.pg_depend 

-- exclude dependencies on system objects:
where objid >= 16384 or refobjid >= 16384 
;
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That code comes from the postgresql wiki, but see also the pg_depend page, and for catalog stuff generally, internals (includes dictionary tables).