How to know the url of installed application on websphere

As mentioned by Michal in his answer, the port can be found in the Administrative console under Servers -> Server types -> WebSphere application servers -> (your server name) -> Ports (in the Connunication section).

The remainder of the URL can be looked up and configured under Applications -> Application Types -> WebSphere enterprise applications -> (your application name) -> Context Root For Web Modules (in the Web Module Properties section).

The port numbers used can be specific to you particular WAS installation and depends on the topology as well. You can either try default 9080 or look for the port number in WAS configuration. What you're looking for is WC_defaulthost for http and WC_defaulthost_secure for https.

If you have access to WAS admin console, navigate to Servers => WebSphere Application Servers and choose your server. Then look for Communication sections which contains Ports.

Of course it is always possible to look for the port number on disk. For example:
<WAS_HOME>/profiles/<PROFILE_NAME>/logs/AboutThisProfile.txt is generated when creating the profile, so contains the port numbers as well. Then you can take a look at <WAS_HOME>/profiles/<PROFILE_NAME>/config/cells/<CELL_NAME>/nodes/<NODE_NAME>/serverindex.xml