A Falling Star

Don't be like me and head straight for the cave, or Kadghar won't spawn, and no matter how many times you kill the mob Yorg won't drop anything!

Take Khadgar's flight, once you land in [zone=7767], head straight out to sea (or die at the hands of 110 mobs just inland) and swim down to the crash site, it's swirly.
Then enter the cave, and get the credit for exploring it
Then kill [npc=112477] and loot the [item=140574] before hearthstoning back to Dalaran to hand the quest in.

Coordinates for TomTom / Paste users are:

/way Suramar 92.0, 61.2 Swim down to crash site
/way Suramar 94.6, 64.2 Cave Entrance - swim in to get credit
/way Suramar 94.4, 67.2 Kill Yorg Murkmouth for Mysterious Lightbound Object

Remember where you went to watch Khadgar move Dalaran? Stand on the blue pedestalin the middle of the room. You will be taken to a chamber where you can meet with Khadgar to turn the quest in.

This quest is available at level 100+, but appears to require a certain amount of your Order Hall Campaign to be completed.

This is the first in a quest chain as follows:

1. 
   
2. A Falling Star
3. 
   
4. Bringer of the Light
5. 
   
6. Light's Charge
7. 
   

Completing these quests unlocks a tint for your Classic Artifact weapon skin.

A Falling Star

This quest is picked up from [npc=90417] in [zone=7502], in the Violet Citadel. After this, you will take a flight path at Krasus Landing that takes you to [zone=7767].

Once you land, you will be on a beach, and you may notice an [npc=103866] or two, and a [npc=103467].

If you are level 108 or less, I would ADVISE AGAINST clicking the banner! This banner is a a Rare mob encounter, which spawns a few waves of mobs, after which [npc=103827] spawns. This banner/mob encounter has nothing to do with the quest!

This is what you want to do instead (make sure to do these steps in order, rather than going straight to the cave!):

1. 
   
2. Search the crash site - head to [92,61.2], which is due east of the island. Swim down to find the area (Looks like a swirly spot in a crevice on the ocean floor)*
3. 
   
4. Investigate the Cave - The cave entrance is at [94.6, 64.2].*
5. 
   
6. Mysterious Lightbound Object - kill [npc=112477] in the cave, and loot [item=140574].
7. 
   

*Watch that you don't run out of breath!

After you return to [zone=7502], you turn in the quest in the Chamber of the Guardian (take the port at the center of [zone=7502]).

Bringer of the Light

The completion of this quest is in spoiler tags, for those who want to figure it out and complete it themselves. I've listed what happens next, as well as tips for completing this quest.

Spoiler

Khadgar opens up a portal to the Exodar, and taking it starts the scenario "In Defense of the Exodar". As with any scenario, you can right-click your portrait and "Leave Instance Group" (even if you are solo) to leave and start again.

1. 
   
2. Step 1 is to find the Prophet Velen in the Vault of the Lights. Just make your way to the area marked on the map, killing demons on the way. If you happen to aggro a bunch, just kite them to Velen, as they will be incinerated by the dome of light surrounding him.
3. 
   
4. Step 2 involves A) Rescuing 12 Terrified Exodar Citizens and B) Destroying 8 Fel Portals.
   
   • 
     
   • All of the portals are marked on the map, and there are many more portals than you will need scattered through the Exodar.
   • 
     
   • When doing this step, its best to skirt your way around edges of the rooms. If you stand in the middle of pathways, the stream of demons running towards Velen can easily aggro and overwhelm you! Find corners and alcoves that avoid the steady stream of mobs that spawn.
   • 
     
   • Beware of patrols, as there are groups of demons all over the place and its easy to get overrun.
   • 
     
   • [npc=109712]s are typically around the edges of rooms, corners, behind structures/boxes, in covered rooms, etc.
     
     • 
       
     • Some are children, so are smaller and easy to miss
     • 
       
     • They are marked on your minimap, so this a great way to track them down
     • 
       
     
     
   • 
     
   • Extra (Optional) Stuff:
     
     • 
       
     • BONUS QUEST: There is an extra quest available from [npc=110695] at 44.8, 9.4 in the Crystal Hall. This grants some gear and XP; it involves surviving 3 waves of demons, then killing [npc=110781] after these waves. As a DPS class doing this, it was quite a challenge! Mobs spawn frequently, and you must rely on the NPCs to help (i.e. stay near them). [npc=110695] will also heal you.
       
       • 
         
       • When you are to face [npc=110781], I would suggest saving all of your DPS cooldowns (or healing, for that matter) for this encounter. The NPCs tank him, so dying is not a concern; rather, if this takes to long, Nobundo will bite the dust and this quest will fail!
       • 
         
       • If you want to complete this optional quest, you MUST pick it up before completing the Step 2 objectives (Portals and Terrified Citizens) or else it will not be available!
       • 
         
       
       
     • 
       
     • There is an (optional) bonus objective active during the scenario (you'll see the objective progress bar). Completing it by killing demons will net you some gold and experience.
     • 
       
     • A rare spawn NPC ([npc=110486]) was found at [59.7, 83.1] in the Trader's Tier. He is surrounded by Felhounds, which can be killed in smaller groups to avoid being overwhelmed.
       
       • 
         
       • He drops [currency=1220 domain=legion] and [item=140533]
       • 
         
       
       
     • 
       
     
     
   • 
     
   
   
5. 
   
6. Step 3 is to return to Velen, and allow him to examine the [item=140574]
7. 
   
8. Step 4 is to escort Velen to the Seat of the Naaru
9. 
   
10. Step 5 involves defeating High General Rakeesh. There is a very interesting reveal that occurs through this - I won't say what it is though!
    
    • 
      
    • Other commenters stated that you can tag High General Rakeesh and let the NPCs kill him, but doesn't appear to work anymore - you have to fight him yourself. That being said, it seems they may have made this encounter more manageable, as the NPCs do help, and will heal you.
    • 
      
    
    
11. 
    
12. After this, simply use [item=140319] to return to Dalaran.
13. 
    

Light's Charge

After completing Bringer of the Light, you receive Light's Charge, which has you return [item=140763] to your Order Hall. At this point you unlock one of the tints for your Classic Artifact weapon skin (part of the criteria for Fighting with Style: Classic).