I can not see any and the original did not, it relied on the swell/expression/volume peddle to achieve volume changes when in use.
Will just have to use automation within your DAW or attach a swell/expression/volume peddle to your controller. The Peddle in the graphic responds to Midi CC 11.
Don't know about cc11 which is expression but on my system the demo responds to cc7 which is volume.
The Vox, like most all organs, is an on/off proposition for notes; a note is either full on or full off. Been that way throughout musical history which is why volume pedals exist and in a pipe organ those pedals actually control the opening and closing of the doors in the wind chamber that supplies the pipes.
The only organ that bucked this was the original Hammond B3. It was not a single key contact but a series of bus bars (9) that each had their own contact so an organist with good touch could activate one bar at a time, bringing the respective drawbar. However this did not control volume, just the sound.
