Here's one way:
***********
String s1 ="this is one";
char[] mychars = s1.toCharArray();
for (int i = 0; i < mychars.length; i++) {
  System.out.println("The current character is: " + mychars[i]);
}

Maybe you mean this? (untested)

public class Grazy {
   public static void main(String[] args) {
       if (args == null || args.length == 0) {
           System.out.println("Give a command line parameter!");
           return;
       }

       System.out.println("\"");
       // The first " is not part of the String ;-)

       char[] chars = args[0].toCharArray();
       for (int i = 0; i < chars.length; i++) {
           System.out.println(chars[i]);
       }

       // Maybe you want it also to end with a "
       System.out.println("\"");
   }
}