What is the default carrier frequency of matlab's pskmod?
The function pskmod.m returns a vector of complex baseband symbols. Each element of that vector has the form $y_k=e^{j(2\pi m(k)/M+\phi) }$, where $M$ is the alphabet size, $m(k)$ is an integer between $0$ and $M-1$ which depends on the message symbol at time $k$, and $\phi$ is some initial phase (which defaults to $0$).

There is no carrier involved, and for simulation purposes it's usually also not necessary to use one because a digital communication system can be simulated by using the equivalent baseband system.