Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Shape
SPOTSHADER_GAP_SHAPE
Parameter: Texture
SPOTSHADER_GAP_TEXTURE
Parameter: Gap Color
SPOTSHADER_GAP_COLOR
Parameter: Spot Color
SPOTSHADER_CIRCLE_COLOR
Parameter: Scale
SPOTSHADER_SCALE
Parameter: U
SPOTSHADER_SCALE_U
Parameter: V
SPOTSHADER_SCALE_V
Parameter: Rotate
SPOTSHADER_ROTATE
Parameter: Shadow
SPOTSHADER_SHADOW
Parameter: Diffuse
SPOTSHADER_DIFFUSE
Parameter: Specular
SPOTSHADER_SPEC
Parameter: Illumination
SPOTSHADER_ILLUM
Parameter: Camera
SPOTSHADER_CAMERA
Parameter: Lights
SPOTSHADER_LIGHTS
Parameter: Specular
SPOTSHADER_SPECULAR
Parameter: Illumination
SPOTSHADER_ILLUMINATION
Parameter: Shadows
SPOTSHADER_SHADOWS
Parameter: Invert
SPOTSHADER_INVERT
Parameter: Use Lights
SPOTSHADER_INCEXC
Parameter: Lights
SPOTSHADER_INCEXC_LIGHTS