I need to move a slave site from JMS to a second server, what is the best method to perform this?

If you want to move an existing slave to make it standalone, you have to backup the DB and backup all the files of your master.

The idea is to replicate your current PHP files where is installed the master and all your slave site.
You restore everything on another server.
Copy the slave site "configuration.php" into the root directory.
The objective is to replace the master configuration.php file with the slave site that should become standalone.
Edit the configuration.php and change the DB connection parameter. Perhaps also change the tmp and log path.

When done and restore the DB with the slave site, try to start the new website.
It should start as a master using the 'slave' configuration.
When done, you can delete the slave site that you have in JMS.
When everything is deleted, you can un-install the JMS patches and after un-install JMS.

Becarefull that if you have used specific image, media, template folder, you will have to move them into the root directory to replace the master content with the slave content.

Becarefull also that the image and media folders are defined in the Global Configuration and that those parameters are saved in the DB. So you have to check those path.

Edit the configuration.php files that is present in the root directory