Add a Pronouns option to the patron registration form, and to the edit options in My Accounts in the catalog so patrons can change this at any time. This could be done by having a dropdown list to choose from, but with so many possible variations and combinations, this would need an Add Other option may just add more complexity, so we would like to see this as a free text field, with a few examples to suggest a format, like she/her/hers, they/them/theirs.
We found this Educause article useful, particularly the section on pronouns: Supporting Students’ Gender Identity: An IT Perspective