You'll have to extract the jars and then do jar tf on each jar to find
what you want. Use some clever shell command to do that depending on
your shell...you'll have to loop over the jars..

jar xf foo.war WEB-INF/lib/*.jar
for i in `ls *.jar`; do echo $i; jar tf $i | grep myClass.class; done

Something like that - I didn't test it, but you get the idea. If you do
this regularly, put it in a script.

Also, I'm sure there is some cute tool or other than can do it.