My attempt at creating the most pain one could experience without looking anything up:
It starts with strapping a man down to a metal grated table (the room must be clean), first you would need to replace his heart with a machine that pumps blood for him (yes it obviously exists) so that their heart wouldn't give out before their brains did
Next we address the possible issue of blood loss, so we will create a separate "heart" for the brain using the same machinery as earlier
Now that we've made sure the subject will not die of a heart attack or blood loss we will prepare a set of disinfected knives to skin him, now this should be done by a professional so as to not make the subject bleed more than necessary
This is also why we chose a grated table, it will hurt more to lay down and if we place a giant bowl below it we could get back the blood we lost, possibly recycling it so that blood loss would be an even lesser issue (this is why the room must be absolutely clean)
Now this much pain is already far too much for an average human to bear but let's say it isn't, what we should do next is not add salt onto the wound as some of you may suggest, it's ultimately short term and the salt could carry some type of microorganism, what we should instead do is stick vinegar coated needles in them
To get these needles we must first boil a small pot of vinegar (call me paranoid but I'm not having them die of anything other than shock) and dip the metal needles into it, this will undoubtedly coat the needles and the heat would provide even more pain
Now after the subject has the needles stuck in them, preferably down to bone(the subject is probably dead by this point, but let's say they're not) we can use them to scrape around at the bone by wiggling the needles, causing great pain and discomfort
after that we can either take the needles out and continue with other things until we're bored or do the grand finale, cooking
Now we can slightly modify the machine that is acting as the heart for the main body, not much is needed all it needs is to have blood temperature be able to be controlled (I know that the machine already does that but I don't if the temperature is able to be controlled)
After the slight modification done by our dear tech engineer we set the temperature of the subjects blood at a nice 70 Celsius or 158 Fahrenheit, now we can watch as they die of shock as they get cooked, their head slowly succumbing to the same fate through heat transfer
I hope this made sense because I truly did not look anything up
Edit: I'll be back with a version 2 because looking it up, there are too many biological problems here that I will address