DOAP is used to share informations (metadata) about a software project. Now that you have a generated DOAP from POM by the DOAP Plugin, you need to publish it and diffuse it.
You need to publish it somewhere where the DOAP file will be accessible via an HTTP or HTTPS request like a web server or SVN.
By default, the DOAP Plugin generates the file in the reporting output directory (i.e. ${project.reporting.outputDirectory}). So, it will be available when you will deploy the Maven site via the site:deploy goal. See Integrated DOAP Plugin With The Site Plugin part for more information.
Several Semantic Web directories like http://doapspace.org/ or http://doapstore.org provide metadatas relating to open source projects into a public catalog. You need to enter the DOAP file URL to their catalogs.
You could also use the Ping the Semantic Web which share RDF data with the World.
Our Maven DOAP file is share on SVN here. Here are the result from some Semantic Web directories: