If you use OpenDJ Control Panel to perform a manual export, the UI will show the syntax of the export command. You can turn that into a script and run as needed.

The GUI is notorious for slipping in unicode characters. So be prepared to replace spaces and dashes in your standard text editor. Also, most double quotes are unnecessary.
D:\PTC\opendj-4.5.4\opendj\bat\export-ldif.bat --ldifFile D:\PTC\WindchillOpenJD.ldif --backendID userRoot --hostName db.ptc-training.ptc.com --port 4444 --bindDN "cn=Directory Manager" --bindPassword password --trustAll --noPropertiesFile