Kinda depends on yer version of controller, but these should cover it.
The Pink w/White dot is one side of the LSC (Left Stick Click) button in every diagram. The other side of the button depends on the version of controller you're using. If you're using that Older Matrix Version controller board like in the pic you posted, then the other side of the LSC would be the Blue w/White dot trace.
That pic is also labeled wrong as the Matrix version of controllers do not have a 'signal' and 'ground' side to the button contacts.
WIRELESS CONTROLLERSOlder Matrix Version Top
Older Matrix Version Bottom
Newer CG Version Top
NOTE: This board is Common Ground and one side of every button is Ground.Newer CG Version Bottom
WIRED CONTROLLEROlder Matrix Top
Older Matrix Version Bottom
Newer CL Version Top
NOTE: This board uses a Common Line (1.8v) for all of the buttons. Newer CL Version Bottom