In the above screenshot, you'll notice that the Dungeon Finder interface has been updated. When you click on the Choose Reputation button, your Reputation tab will appear. Choose the Pandarian faction you want and click Find Group. You can only cash in on this reputation reward once per day.
My main has hit exalted with most of the factions. I'm still working on the Anglers but I have a hard time motivating myself to push for it. Work orders and the reputation rewards in the dungeon queue should help ease that grind up. I feel the same way with my alts. I have absolutely no interest at the present in doing all those dailies again (at least, not for a long time).