Rukil's Apprentice
This is a simple fetch-and-retrieve mission. Once Rukil clues you in to the fact that his apprentice is missing, search for her to the northwest of the Undercity settlement. Bring the journal you find on her corpse back to Rukil to open the Promised Land quest.
The Promised Land
Rukil asks you to bring him the journals of his father and grandfather, in the hopes that they, together with the clues in his apprentice's journal, will provide some answer to the riddle of the Promised Land. Both can be found on skeletal remains in the sewers.
Light side Solution: Find the journals and return them to Rukil. Everyone in the village will leave for the Promised Land, including the healer and the merchant, so you may want to postpone completing this quest until just before you enter the Black Vulkar base in the sewers.
Dark Side Solution: Bring the journals back to Igear, who wishes to destroy them, since he fears that his business would be destroyed if everyone left the settlement.
Rakghoul Serum
Talking to Zelka Forn in the Upper City medical facility, you'll hear about a horrific plague that is sweeping through the population of the Under City. Apparently, it transforms a normal, healthy human into a ghoulish monster, interested only in killing. Zelka will inform you that the Sith patrols in the Under City may have an experimental serum that he could synthesize into a cure, but his assistant, the appropriately named Gurney, wants you to sell the serum to a gangster named Davik Kang for 1,000 credits.
(You can also pick the locked door in the medical facility to find some Republic Soldiers in Bacta tanks. If you threaten to tell the Sith about it, you can force Zelka to hand over 100 credits, and earn some points towards the Dark side. If you keep his secret, you earn Light side points.)
The Rakghoul serum is found on the body of a Sith soldier in the Under City, to the east of the settlement there. Once you kill the Rakghouls guarding his body, you can grab the serum and do with it what you will. Before you dispose of the serum, don't forget about the infected outcasts quest that can be completed in the Under City settlement.
Light side Solution: Track down the serum in the Under City and bring it back to Zelka.
Dark Side Solution: Take the serum to Zax in the Lower City Cantina and sell it to him for a tidy sum.
Infected Outcasts
If you speak to the healer in the Under City settlement, she'll let you know about a group of infected Outcast villagers that have been quarantined nearby. If you do get the Rakghoul Serum, you can enter the quarantine cage and heal two of the infected villagers, gaining a few Light side points, or just kill them. You'll retain enough of the serum to complete the main Rakghoul serum quest.