We expose transaction logs as MBeans:
You can use an MBean viewer such as jconsole and navigate to the bean with the name jboss.jta:type=ObjectStore. From there you need to run the "probe" operation which should then populate the jconsole window with nodes corresponding to the transaction logs.
In AS7 the supported method is via the cli:
> bin/jboss-cli.sh --connect
> cd /subsystem=transactions/log-store=log-store
> \:probe # colon probe (ie not an emoticon)
the probe operation exposes any prepared transactions (and the participants involved in those transactions)
To see the documentation of what the nodes and attributes mean read the resource description (recursive=true gives you everything under the current node):