Can the bones from picnics, butts, and ribs be used to make pork stock or have they already been exhausted of all goodness after smoking?

You won't get a lot out of the blade bone (butt); the others you mention fare a bit better but are insufficient in themselves--you have to add to them.

When you say add to them, do you mean using them along with uncooked bones? Just trying to get as much as I can out the pig.

Yes, well, uncooked and/or those you've stashed, cooked, from other meals. 'Cooked' in this case could mean other bones from other smoking sessions, grilling sessions, roasting. Depending on what the point if the stock will be, it can be good to use cooked and uncooked, and can be good if some meat is left on them. Pork neck bones are good additions (and are often cheap).

I've used leftover skin, fat & bones from a shoulder cook to make stock for pea soup. I have never seen pea soup disappear so fast in my life.

The bone and and bits of meat still attached from a fresh ham is great too. This is a favorite use.