It should be in JBOSS_HOME/standalone/deployments see there
If you deploy a war file name as 'sample' then you could see this file domain/configuration/domain.xml as
[...]
<deployments>
<deployment name="sample.war"
runtime-name="sample.war">
<content sha1="dda9881fa7811b22f1424b4c5acccb13c71202bd"/>
</deployment>
</deployments>
[...]
<server-groups>
<server-group name="main-server-group" profile="default">
[...]
<deployments>
<deployment name="sample.war" runtime-name="sample.war"/>
</deployments>
</server-group>
</server-groups>
[...]
ls domain/content/
|---/47
|-----95cc29338b5049e238941231b36b3946952991
|---/dd
|-----a9881fa7811b22f1424b4c5acccb13c71202bd
This works for standalone/content as well.
Note that in the standalone.xml file, as referenced above, the sample.war file has a hash. The hash is the key to locating the WAR file. You will not find it by searching for "sample.war" in the 'content' directory though. First 2 characters of hash is parent directory. The rest is the directory containing the WAR file. However the WAR file has been renamed to 'content'
|---/47
|-----95cc29338b5049e238941231b36b3946952991
|---/dd
|-----a9881fa7811b22f1424b4c5acccb13c71202bd
|-------content <-- this is really sample.war file. JBoss renames it. (go figure!)
do a jar -xvf content and you will see all the class, web.xml, etc files for sample.war