Sonia Sotomayor asked herself what new thing did she learn at the end of every day. If she couldn't think of something then she remedied the issue by reading something. (Meltzer2018)

While it's not known if she wrote notes about what she learned, doing so may have allowed her to accumulate a heck of a zettelkasten practice. Many people mistakenly think that they need to be creating dozens of perfect permanent notes for their zettelkasten every day, but in reality, most historical practitioners only made one or two each day. It's the accumulation and links between them that turn them into a more valuable collection over time.

Meltzer, Brad. I Am Sonia Sotomayor. Illustrated edition. New York: Dial Books, 2018.