There are two general approaches to publishing content that is in Alfresco Content Services / Alfresco Community Edition through a web portal like dotCMS:
1. Push the content from the Alfresco Content Repository to the web presentation layer
2. Pull the content from Alfresco through a search
1 is often triggered by a "publish" event, and often involves using the FSTR or replication service. This is fairly complex and not very flexible.
Most people pursue approach 2, and include in the search query a check for a "published" aspect, or some other marker that the content is ready to go live.
In general, you can query the content from Alfresco using the industry standard CMIS APIs, or using the Alfresco specific REST APIs. This can be done from a customization in the web portal, or through an independent service that pulls from Alfresco and pushes into the web portal.
I suggest your next step is to check if dotCMS has a CMIS connector of some sort.
