Talk to ToniliaEdit
Once the Dragonborn has turned in three of the Special Jobs to restore the Thieves Guild, Tonilia will ask them to deliver a package of Moon Sugar to a Khajiit named Ri'saad and ask him to deliver goods for the Thieves Guild.
This quest will appear in the miscellaneous quests section of the Journal.
Meet with Ri'saadEdit
In order to complete this quest, the Dragonborn must track down Ri'saad and his caravan. If the map marker for the quest in enabled in the Journal under miscellaneous, his position will show up - probably on the road between cities. The Dragonborn can intercept him manually or figure out his next destination and Fast Travel there to beat him. Once found, talk to him to complete the quest.
Return to ToniliaEdit
Return to Tonilia to turn in the quest, she will praise the Dragonborn for making the deal and give a small sum of gold as a reward.
Note: there is no actual "Quest complete" stage of the journal for this quest.