Question

See it   Why is the part of the nepenthese where it's forming black in the upper right corner

Answer
That's a new shoot developing from the main stem.  New shoots tend to be a bit more sensitive to fluctuations in the environment.  Typically they will form near the base of the plant where they are more protected.  When they form in the upper stem, they're more exposed and become susceptible to damage.  This is minor and doesn't at all affect the overall health of your plant.  It only affects the appearance.  You can cut off the shoot if it's appearance bothers you.  Other than that, there's not much you can do about it.  The damage is already done.  It's likely you have more shoots forming elsewhere on the plant, so cutting it off isn't a big deal.

Good growing!
Jacob Farin