See the relevant product datasheet for an exact figure. If using the potentiometer in the 3-terminal potentiometer mode (without any series resistor), the tolerance is irrelevant because the resistances, RWA and RWB, are ratiometric. If using the potentiometer in the 2-terminal rheostat mode, account for the worst-case variation.
On some nonvolatile digital potentiometers, resistance tolerance is stored in the memory at the factory with an accuracy of 0.1%. Thus, users can retrieve the resistance tolerance and calibrate the system accordingly.