How do i see the border?

What plugin are you using?

 

That's world border I'm assuming. You can set how the border looks in the config.

 

If i'm not mistaking, with the WorldBorder plugin that you are using, it will not display the border.

 

if you are running an 1.8+ server, by default you have the command /worldborder set 10000 10000

 

You can also set the worldborder in server.properties and the border will be visible.