It's called "commonfuckingsense."
there is a test you can have done at a hospital, they stick needles in your arm and leg, then they send electric shocks to you and a machine reads the response your nerves give and that is how you will know if you feel the same/more/less pain than everyone else.
There is no way to know for sure.
Because we're all human and our internal machinery isn't different. We all have a circulatory system, liver, etc. Plus, we can communicate with each other about how we feel and figure out similarities. Even if I've never met you, I know stabbing you in the heart will most likely kill you. That's how I know we're alike (but each individual has different characteristics). Hopefully that makes sense.
What kind of pain Physical or Emotional.