They are the "reacquisition" daily quests.

In Hew's Bane (which apparently is currently the only place you can do them and have them count for this challenge) you pick them up from the bulletin board outside the Thieves Den, in the city (not outside the city), by the bearded man sitting near the entrance to the Thieves Den. The blue quest pointer on the bulletin board should help you find the location if you haven't seen it before. When you turn in a quest to him, sometimes he'll say someithing like "A fine day for finding," although the quests are called "reacquisition" quests. Two of the daily quests involve the two world bosses in the zone (although you don't need to kill the bosses to complete the quests), and two of them involve the two delves in the zone.

I'm not sure about the ones in Glenumbra, as I haven't started doing those dailies yet, but I believe the quest pointer is inside the Glenumbra Thieves Den.

I rerolled it. 24 daily quests are not worth it.