The syntax is
\scale-diagramm #'( (string1 fret1) (string2 fret2) ... ) #notesinscale #size
For example for a c pentatonic scale (first six notes)
\scale-diagramm #'((5 3) (5 5 ) (4 3) (4 5) (3 2) (3 5)) #5 #1.5
you can wrap this up in a markup command for building up a list of scales
cpenta = \markup \scale-diagramm #'((5 3) (5 5 ) (4 3) (4 5) (3 2) (3 5)) #5 #1.5
and use it like this
c^\cpenta d f g a c
The snippet doesn't show it, but the (1) position of the scale is inverted