lvl 25 ses quest: just go to hometown bindstone npc and talk with him
lvl 40 ses quest: complete all your solo quests (seek for solo quests on google) from lvl 1 up to 40. Only then you can obtain your ses quest at the npc in Lauke's Monastry. You have to kill the boss at the end of Lauke's. Be aware that it's a magic attacking, debuffing lil bish and you might want the help of a higher lvl player. Preferably templar. I killed it with a priest once, but that takes some time..
lvl 50 ses can be obtained in Pine map (that bindstone near that dungeon i forgot the name of, similar to Black Dragon Sanctuary), for that you have to kill Serpenter Caliphs. Those, too, are magic attackers and you might want some help if you're squishy. This quest can be done without doing your solo quests.
lvl 67 ses quest can be obtained by some npc in perishing plains map. (not the one at the bindstone near scarecrows but the one further down the map, just follow the same road all the way down). For this you'll see a road going like "@" just follow that spiral all the way down and you'll find a chest, open that chest - kill the boss and.. done.
Hope it somehow helped, i can't recall all the names by heart or names of the places so ehm yeah. I'm also not ingame and don't have much time (need to leave the house in 10 mins), so hope it helped for at least some bit.