Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: UVs
OBJEXPORTOPTIONS_EXPORT_UVS
Parameter: Normals
OBJEXPORTOPTIONS_NORMALS
Parameter: Vertex Colors
OBJEXPORTOPTIONS_VERTEX_COLOR
Parameter: Flip X Axis
OBJEXPORTOPTIONS_POINTTRANSFORM_FLIPX
Parameter: Swap X and Y Axes
OBJEXPORTOPTIONS_POINTTRANSFORM_SWAPXY
Parameter: Flip Y Axis
OBJEXPORTOPTIONS_POINTTRANSFORM_FLIPY
Parameter: Swap X and Z Axes
OBJEXPORTOPTIONS_POINTTRANSFORM_SWAPXZ
Parameter: Flip Z Axis
OBJEXPORTOPTIONS_POINTTRANSFORM_FLIPZ
Parameter: Swap Y and Z Axes
OBJEXPORTOPTIONS_POINTTRANSFORM_SWAPYZ
Parameter: Flip Faces
OBJEXPORTOPTIONS_FLIPFACES
Parameter: Resolve N-gons
OBJEXPORTOPTIONS_TRIANGULATE_NGONS
Parameter: Objects as Groups
OBJEXPORTOPTIONS_OBJECTS_AS_GROUPS
Parameter: Material
OBJEXPORTOPTIONS_MATERIAL
Parameter: Default Material
OBJEXPORTOPTIONS_DEFAULTMATERIAL
Parameter: Invert Transparency
OBJEXPORTOPTIONS_INVERT_TRANSPARENCY
Parameter: Frame Range
OBJEXPORTOPTIONS_ANIMATION_TYPE
Parameter: Start Frame
OBJEXPORTOPTIONS_FRAME_START
Parameter: End Frame
OBJEXPORTOPTIONS_FRAME_END
Parameter: Frame Step
OBJEXPORTOPTIONS_FRAME_STEP
Parameter: Shared Material File
OBJEXPORTOPTIONS_SHARED_MTL_FILE
Parameter: Export as UTF-8
OBJEXPORTOPTIONS_ENCODING_UTF8