How to make Kindle Preview run on El Capitain
I found this works 
(from Apple's Java support note )

1) Download and install X11
https://xquartz.macosforge.org/trac

2) Download and install Java for OSX
https://support.apple.com/kb/DL1572?locale=en_US

3)
finder>applications>(right click) kindle previewer.app>show package contents>contents>macos>
(Right click) Launcher>open with> other, choose textedit, then enter the following and save

#!/bin/sh

export JAVA_HOME="/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home"

dir=`dirname "$0"`
cd "$dir"
classpath=./:./lib/touchLibs/etc/fonts/fonts

for i in `ls ./lib`
do
classpath=$classpath:./lib/$i
done

export DYLD_LIBRARY_PATH=.

# start the previewer
fileExtT=`echo $1 | awk -F. '{print $NF}'`
fileExt=`echo $fileExtT | tr '[:upper:]' '[:lower:]'`

if [ "$fileExt" == mobi -o "$fileExt" == azw3 -o "$fileExt" == epub -o "$fileExt" == opf -o "$fileExt" == html -o "$fileExt" == zip ]
then
# opens only the first book in command line. TODO: handle multiple books in command line
${JAVA_HOME}/bin/java -d32 -XstartOnFirstThread -Dfile.encoding=UTF-8 -cp "${classpath}" com.amazon.epub.reader.Main "$1"
exit 1
else
${JAVA_HOME}/bin/java -d32 -XstartOnFirstThread -Dfile.encoding=UTF-8 -cp "${classpath}" com.amazon.epub.reader.Main
exit 1
fi


4)
(Right click) KindlePreviewer>open with> other, choose textedit> then enter the following and save

#!/bin/sh

export JAVA_HOME=/usr/libexec/java_home -v 1.6
# start the autoupdate 
java -jar autoupdate.jar

./Launcher $@

dir=`dirname "$0"`
cd "$dir"
classpath=./

for i in `ls ./lib`
do
    classpath=$classpath:./lib/$i
done


# start the autoupdate  
java  -jar autoupdate.jar

./Launcher $@