To give someone a rep point, you just find there name in a post or thread and look in the top right along the red bar across from there avater.
You should see some scales click that to give a rep point.
I think i saw in the mods control panel that rep points can be set to always display, but its currently off. I'm betting DLD or Lightning could turn it on.
I think the rep points thing creeped in during one of the last board upgrades