CREATE OR REPLACE FUNCTION Quoted_String (
    n_String       IN VARCHAR2)
RETURN VARCHAR2 -- Quoted string
AS
    l_Prg_Name VARCHAR2(30) := 'Quoted_String';
    o_String VARCHAR2(32767);
BEGIN
    o_String := ''''||REPLACE(n_String,'''','''''')||'''';
    RETURN o_String;
EXCEPTION
    WHEN OTHERS THEN
        RETURN SQLERRM||' in PL/SQL '||l_Prg_Name;
END Quoted_String;
/

SQL> CREATE OR REPLACE FUNCTION Quoted_String (
  2      n_String       IN VARCHAR2)
  3  RETURN VARCHAR2 -- Quoted string
  4  AS
  5      l_Prg_Name VARCHAR2(30) := 'Quoted_String';
  6      o_String VARCHAR2(32767);
  7  BEGIN
  8      o_String := ''''||REPLACE(n_String,'''','''''')||'''';
  9      RETURN o_String;
 10  EXCEPTION
 11      WHEN OTHERS THEN
 12          RETURN SQLERRM||' in PL/SQL '||l_Prg_Name;
 13  END Quoted_String;
 14  /

Function created.