The question is not a duplicate for that reason, but it does not show the questioner's attempt at research, and more importantly to me it may even be General Reference, so I do not think the community should cast votes to reopen it. In my general reference check, the first thing I thought to check is master degree plural possessive and I found the Johns Hopkins Bloomburg School of Public Health's style guide as my third result on google, which has the following advice:
Multiple master of arts (or master of science) degrees
Under no circumstances is the form "masters" (an "s" with no apostrophe) appropriate.
Use the plural form as follows:
I have master of arts degrees in English and history.
I have masters' degrees in English and history.
The School offers masters' programs in public health, health science and health administration.
The second example seems to demonstrate that the plural possessive form of masters' would be used for multiple degrees, even if there is only one possessor.
Right now I would rather not reopen a question just to risk having what may be a general reference answer posted to it. Are there more reasonable search terms that would be more likely to be used in a cursory search, or do you find that answer to be inadequate in some way? Do you want to post a better answer? If you can explain why you think it is not general reference despite this cursory check, then I will consider casting my vote, but otherwise I do not think the question should be left open long enough to post an answer, and the community is slow to close questions that should be closed.
Maybe a moderator could reopen the question and swiftly reclose it, so that the right closure reason shows and people are not redirected to the wrong target question.