Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Strength
MGTARGETEFFECTOR_STRENGTH
Parameter: Selection
MGTARGETEFFECTOR_SELECTION
Parameter: Target Mode
MGTARGETEFFECTOR_MODE
Parameter: Set Weight
MGTARGETEFFECTOR_SETWEIGHT
Parameter: Target Object
MGTARGETEFFECTOR_OBJECT
Parameter: Use Pitch
MGTARGETEFFECTOR_PITCH
Parameter: Reverse Heading
MGTARGETEFFECTOR_REVERSEVECTOR
Parameter: Up Vector
MGTARGETEFFECTOR_PRIMITIVEAXIS
Parameter: Object
MGTARGETEFFECTOR_UP
Parameter: Repel
MGTARGETEFFECTOR_REACT
Parameter: Distance
MGTARGETEFFECTOR_RANGE
Parameter: Distance Strength
ETARG_RANGE_STRENGTH