This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one for details.
I don't know about web-console (it has not been working in the latest releases), but using jmx-console, in the jboss.jca:name=XXX,service=ManagedConnectionPool MBean (where XXX is the datasource name), you can find these attributes:
ConnectionCount - current number of connection to the database InUseConnectionCount - the number of those connections that are active (in use by some app)