Let us make a quine maker!
J - 73 char

Takes input on stdin, as the 0-origin index in characters and the source, separated by a newline. Introduces a copy of the program at the specified point as a string.

((".@{.~({.,}.,~'(',')',~(LF;''',LF,''')rplc~quote@])(}.~&gt;:))i.&amp;LF)1!:1]3


Explained by explosion:

(                                  )1!:1]3  NB. stdin
 (                           )i.&amp;LF         NB. find the first newline
     {.~                                    NB. the index part of input
  ".@                                       NB. convert index to integer
                      (}.~&gt;:)               NB. the source program part
        ({.,}.,~     )                      NB. program before and after index
                ...@]                       NB. program quoted properly


For example, given input

3
abcdef'ghij'
kl mn 0p1


the output is

abc('abcdef''ghij''',LF,'kl mn 0p1')def'ghij'
kl mn 0p1


because J uses Pascal-style strings: 'Isn''t this great?'