How can I get it so when someone +reps someone for a post, it shows that a user was granted +rep from the user who gave him rep on their post. Kinda like the "thanks plugin", but for +rep
Impossible without a plugin. I'm not even sure if MyBB has hooks on these actions.
The only plugin there was for this was Tomm's MyNetwork Post Reputation. However, he has closed the MyBB section of his site and the plugin is no longer available.