Long story short, a Taekwon Ranker is a Taekwon that stays a TK Boy/Girl forever but competes to gain entry to the Top 10 Rankers. You can use /taekwon to access this list.
This is done by utilizing Taekwon Mission as found here:
http://ratemyserver.net/index.php?sk_name=Taekwon+Mission&page=skill_db&sk_search=SearchDue to the great adversity of many monsters as well as the somewhat high #s on the list (well, I've seen more, but 200-300 points is still a lot of effort to put in) it's more of an attempt to experience the world of rising up the overall ladder rather than an attempt to enter the top ranking. But hey, who knows, you might just make it somehow. =X I also don't recommend doing this until you get a few good gears to work with, some monsters are just plain brutal to fight against.
As you can see at the bottom of the skill, the caveat of getting into the list is actually quite interesting. Disregarding how the balance on the server kind of shafts the TKs in certain ways, they are actually pretty scary in their own right. Rankers get HP/SP modifiers that mark them pretty high up compared to other jobs, and they don't even need a weapon since they can spam kicks endlessly.
It's more about the journey than the end for this style. Go for broke! </Capcom>