When you say "the top right corner of the screen" do you mean in the list of all your current missions? Hit "L" to see the list of missions you have and check to see if you are still 'tracking' the mission. That could be why you don't see the marker for the trainer. If it's untracked, click the button to track it then check the map again.
If the quest is gone from your list somehow you should be able to reacquire the quest. The quest giver should be right near the Tython/Ord mantrel shuttle. Here is a SS I found doing a random search that's probably more helpful than describing it.
The Jedi Knight trainer himself is in the combat training area. He's in the first cubby on that outside ring, nearest to that Tython shuttle.
You defiantly don't have to re-roll. If it still isn't working I'm sure sending in a ticket would do the trick, they'll probably re-set the quest for you.