[Locate the WM8975 CODEC to the middle left above the two yellow components.] You can either take the audio feed from either the top (north) of C86 and C87 there, or above the C53 and C54, the two black elements with the Z printed on them. The sound is exactly the same from either one, but the C53 and C54 pair can be inverted to feed a speaker (invert the C54 line). Feeding them straight to your DC blocking caps to your stereo jack would be the same setup for both pairs. Send the signals to the positive lead of a 1uF cap and straight to the headphone jack. Now the datasheet says to put 100ohm resisters after the DC blocking caps to protect from improper usage, but I didn't want to degrade the sound with noisy resistors since I won't be letting anyone use my iPod anyways (who would want to with the way it looks?).
Starting from C86, that's pin 12. Going counter-clockwise, 12 is LOUT1, 13 is ROUT1, 14 is HPGND, 15 is ROUT2, 16 is LOUT2. All this can be gathered from the datasheet
, and page 37 will carry the bulk of the information. All the grounds on the WM8975 will have the same voltage, so you can use any ground associated with the chip. I tried soldering my ground wire to the same ground supply as the chip on the LCD side of the 4G iPod board. I soldered it to a tiny SMD capacitor, so it kept falling off. I compromised with a poke-and-listen approach that encouraged me to disable the clicking sound feature. A fun consequence of using external-to-the-iPod-casing caps is that you can still use your LODs. I won't imagine you will, but if you want to use a Bose Sound Dock, the option is there.