which notation correctly describes the patient with this karyotype?

the correct answer is 47,XY,+21

Explanation:

To figure out the answer to something like this you'd count the total number of Karyotypes that are listed, in this case there are 47. next you'd look at the last karyotype and see what letters are listed under it, which is XY, last you find where the extra karyotype is, which is karyotype 21.

so with all that info put together you get the answer 47,XY,+21