Alts that want Sparks of Shadowflame will need to complete the start of the Patch 10.1 campaign on every character to unlock the weekly quest as there is no skip available.
Spark of Shadowflame QuestThe Splintered Spark of Shadowflame can be obtained weekly from the PvP Weekly in Valdrakken or the A Worthy Ally: Loamm Niffen quest. Unfortunately for players that don't like to PvP, this means that you need the A Worthy Ally: Loamm Niffen quest which unfortunately is locked behind the Patch 10.1 campaign. A Worthy Ally: Loamm Niffen only unlocks after completing Chapter 1 of the story, which also happens to be after your get the first big reputation bonus of 2,500. This means that every all alts will need to complete this intro to unlock Spark of Shadowflame. We're not sure if this is intended as the Zaralek Caverns blog mentions that:
Blizzard]...] concluding the «Breaking Ground» chapter of the Embers of Neltharion campaign opens up repeatable content in Zaralek Cavern for other characters on your account.This doesn't seem to be the case as A Worthy Ally: Loamm Niffen is supposed to be repeatable weekly content.
Patch 10.1 Campaign RequirementsIf the Patch 10.1 campaign isn't available to you, this is because you haven't completed the Patch 10.0.7 Return to Forbidden Reach storyline. Fortunately for alts, there is a skip for Patch 10.0.7 but for people returning to Patch 10.1 right now, they have to go complete some old content first.
Read more on wowhead.com