
What you can see is the top end of a spoke.
Take the wheel off.
Take the tyre and inner tube off.
Take the rim tape off - the yellow tape. (Carefully, unless you decide to replace the tape (looks like a good idea to me)
Use a file to grind down the spoke end to the level of the nipple.
Check the rest of the spoke ends (and file any down that are sticking up).
Replace rim tape, tyre and inner, and inflate.
Ride and enjoy.
Edit:
@mjr may be right and the nipple has failed though with the spoke previously in tension, why would it stick up like that?. Pluck that spoke and the ones next to it and see if the tension is different.