In Leonardo da Vinci's The Last Supper, a woman, has something in her hand. Does anyone know what it is? ?

There is no woman in this painting, so no one can really answer your question. "The Da Vinci Code" wrongly says John, at Jesus' right, is a woman. In paintings of the period, John is portrayed as young, fragile and somewaht androgynous. Look at other paintings of the 1400's and 1500's and see that this is true. Leonardo began this painting about 1495 and used an experimental oil-based fresco medium on this painting, so it soon faded badly. Visari reported in 1566 that the painting was mere blotches, and by 1646, visitors said the subject of the painting could not be recognized. What we see now is mostly 18th Century restoration, so various things may have been added to it. It is not possible to say for certain what John might have in his hand, if you mean him, since there is no woman in the painting. Some etchings of the painting show John with clasped hands, so it is not likely he had anything in them. On a TV show from National Geographic, there is something blue where his hand should be. Several dishes are that color. I do not know what version of the painting this is. Most I see have just clasped hands. I looked at some of Leonardo's sketches for the painting, but he probably changed them before painting them. He spent 3 years or so on this painting, including months on sketches before he painted a stroke.