It is not possible. It is possible.
Work Step by Step
Equation 23.9 gives the potential energy of 2 point charges. For any finite separation, the potential energy is nonzero, and it is not possible to make it equal zero unless $r=\infty$. Equation 23.11 gives the potential energy of 3 point charges as a sum of 3 terms. If the three charges are not all the same sign, one term will be positive and the other 2 terms will be negative. For any configuration, the charge values may be adjusted so that the 3 terms cancel, and the potential energy is zero.