I'm able to follow along and compile the plugin, however I don't know where to place the resulting object file.
The tutorial says:
After placing the resulting test.so file in /usr/lib/lxpanel/plugins (the place may be different depending on your distro, look where LXPanel puts other dynamic plugins), restart the panel (using lxpanelctl restart), then right-click on the panel and attempt to add a plugin to the panel
My system didn't have that directory, so I created it. However, the plugin still doesn't appear in the list of available plugins after copying the object file and "restarting the panel". I'm pretty certain I need to copy the object file to a different location, but I'm not sure where that is or how to find it.