You must recruit Gadd and Oola before you can finish this quest with Renk in his Laboratory. Recruit Gadd with quests Finding Gadd (from Lork in Vlox's Falls) and then Finding the Bloodstone. Recruit Oola with quests Lab Space (from Livia in Vlox's Falls) and then The Elusive Golemancer.
To get to Renk's Laboratory, start in Rata Sum and head south through the Magus Stones. You should not encounter many enemies beyond spiders and weavers. Enter the Alcazia Tangle from there, and continue heading south. You can make it to the entrance to Renk's lab without encountering any enemies at all, if you are good at maneuvering.
The next part takes some careful maneuvering as well. Renk will be surrounded by some Destroyers, and if you move close to them and Renk, you will say something along the lines of "By the gods! Hang in there, Renk!". Once this happens, the Destroyers will move in and attack Renk. If you aggro the Destroyers without your character calling out to Renk, they should only attack you, allowing you to kill the Destroyers and then talk to Renk. If Renk dies, after you kill the Destroyers he will be resurrected if you are close enough to him and you can still talk to him, so do not give up when Renk dies, just keep close to his corpse.