the port SubGit uses to connect to SVN server depends on your setup and the protocol that SVN server uses. For example, if the SVN server is set to use web-server to share access and thus HTTP/HTTPS protocols are used to access the SVN server, then the ports are 80 or 443; yet those are standard default ports that can be overwritten in web server configuration. If SSH (svn+ssh) is used to access the SVN server, then the default port is 22, yet again, this can be changed in ssh settings. For SVN protocol default port is 3690.
All those ports can be changed in the SVN server settings, not in SubGit. SubGit only uses the port that is set in SubGit configuration file in a particular repository (in svn.url setting).