Lymph nodes are like a body's filters. They filter out bacteria and viruses. That's why, when someone is sick, they can have swollen lymph nodes, because they are fighting so hard to get rid of the sickness. Tonsils are a lymphoid organ too. When they swell, people have to get them removed.
I know that papulation is the production of papules. Papules are like pimples. But I don't know what palpate in that sentance means. Sorry and good luck.
I'm not sure about palpating the stomach, but I'm pretty sure that lymph nodes are the pretty much the same for everyone. They're located in the back of humans' necks, by their ears, throat, chest, and underarms. They're probably in similar spots for pigs. Hope I was of some help, and I'm sure if your vet is good, he/she will know where they are on the pigs' too. Good luck!
There are lymph nodes all over the place for guinea pigs. The ones you should be most vigilant about checking are in the chin. There shouldn't be any swellings in the chin at all.
Palpating is feeling around, not necessarily lightly. It seems to be the most offensive part of a vet visit for my pigs.