correct psilocybin molecular structure
Clearly, it cannot be an $\ce{O+}$, as that would require a triple bond to the oxygen, making the phosphorus in the middle quite unhappy.

Of the other two alternatives, both are correct -- however, it matters what environment you're considering the molecule. In neutral or slightly basic conditions, it will be an $\ce{O-},$ while in slightly acidic conditions, it will be an $\ce{OH}.$

Let me know if you need any clarification on why this is the case -- I have no idea what your level of knowledge is.