The UNI/O protocol was created by microchip and is a 1 wire bus.
Not specified by the protocol so dependent on the devices being used.
A pull up resistor is not required but advisable so the bus is idle if the master is not driving it. The value is dependent on bus voltage and other factors – see here. Based on the calculation is this datasheet:
5V bus, Rpmin = 15K33, Rpmax = 150K
3V3 bus, Rpmin = 9K666, Rpmax = 99K