SQL> SELECT 'grant select on '||owner||'.'||object_name||' to scott;' "COMMAND"
  2    FROM dba_objects
  3   WHERE object_type IN ('TABLE', 'VIEW')
  4     AND owner       IN ('HR', 'SH', 'OE')  -- List schema names here
  5  /

COMMAND
--------------------------------------------------------------------------------
grant select on HR.REGIONS to scott;
grant select on HR.COUNTRIES to scott;
grant select on HR.LOCATIONS to scott;
grant select on HR.DEPARTMENTS to scott;
grant select on HR.JOBS to scott;
...