There are so many themes in the Joy Luck Club. In fact, there are so many of them that I will have to limit my answer to three them.
First, there is the theme of inter-generational communication. What makes this even more complex is that the mothers have a mentality from China and the daughters have a more distinctly American mentality. So, there are also cultural themes that come into play. How does one culture interact with another? This is a great topic to discuss.
Second, you will recall that there are also snippets about the various marriages. So, we can say that another theme deals with relationships between husband and wives of men and women. This theme would be more universal.
Finally, there is the theme of the interaction between women. June and Waverly's relationship is a microcosm of the relationships the other women have to face.