Build a small family tree from the code chain.
N is mother of A, so N sits one level above A. A is father of B, so B sits one level below A. B is sister of D, meaning B and D are siblings on the same level, both children of A and N.
This fixes N as the grandmother of D through A, which is a certain fact. What is not fixed is the gender of D. The clue "B is sister of D" only tells us B is female; it says nothing about whether D is male or female.
Since the options split the answer into "Grandson" and "Granddaughter" as separate choices, and gender data is missing for D, neither can be picked with confidence.
\[\boxed{\text{Cannot be determined}}\]