There's no chain on the chainring.
So at a guess it's running something like a 30/39/50 triple upfront for 4 extra gears.
The 20t difference between rings is the max capacity of the Rohloff chain tensioner.
A 16t sprocket is the biggest recommended with a 30t chainring and gives a range with the triple of roughly 13"-115" gear range.
That what I would do with that type of simple setup.
Luck ...........