Zumo is the tradename for the Pololu mini-Sumo robot. A Mini-Sumo robot must be less than 10cm square and weigh less than 500 grams. Any height is permitted.
Pololu provide two main types of Zumo: one functioning as a "shield" for an Arduino microcontroller board, the second, a newer version with an integrated Arduino-compatible controller, which also includes encoders and a few other nice features.
When wiring up a pair of Hall effect encoders to the Zumo Shield for Arduino you'll find that the documentation 1 for the quadrature encoders on the Zumo 32U4 states:
On the Arduino Shield for Zumo there is no pin "PE2", so you'll just have to choose any available (unused) digital input pin for channel B of the left encoder.