Re: Where EXACTLY to lubricate double pedals?
Any section where one part moves against another. The hinge on the footboard is a good example. As is the point where the chain connects to the top of the footboard. After that, it'll basically come down to anywhere that squeaks. Don't over think this though mate. It's something that only has to be done once in a blue moon when things start making noise. I've had pedals last for years before the need to lube, so it'll just depend.
I use a drop of sewing machine oil. I've seen all sorts of wonderful concoctions suggested. Pick one that tickles your fancy. As long as it lubes, it'll be good to go.