You would need a sustain pedal. Make sure you buy one which is either normally-open or is switchable between normally-closed and normally-open. On the Mk1 keylabs, there was a configuration option in their menus to adjust the units for either type of pedal. I'm not sure if this functionality was excluded from the Mk2's firmware, so to save you any heartache, it's probably just best to make sure any pedal you buy is capable of being normally-open.
Avoid pedals described as being 'for Yamaha' or 'for Roland' unless the specifications/instructions also explicitly make it clear that the pedal is switchable between normally-closed and normally-open, because modern Yamaha and Roland workstations and synths require normally-closed pedals.
