I was able to turn in the quest after completing the TWW intro quest (early access) and then use my Dalaran hearthstone toy to go back to Legion dalaran. I was able to pick up the next quest although I have not done it yet so more stuff might be broken still.
For me, I also see 3 different Khadgar’s in Dal. The one that should let me turn it in is in the portrait room, but doesn’t engage regarding the quest. Only lets me asks questions and play a movie (not TWW).