- I can't turn in the quest "Weigh Anchor" because the NPC is not there.
Both Orgrimmar and Stormwind can be in several different phases based on your character's progress. Weigh Anchor (A/H) is part of the Legion introductory questline. If either Walcott Sutton or Kruda Thunderhand is missing for your character, your phasing will need to be corrected by completing other quests in the area.
If your character is level 110 or higher and has started but not completed the Battle for Azeroth introductory questline, you will need to complete that questline to correct your phasing before you can turn in Weigh Anchor.
If your character has started but not completed the questlines to open up the Cataclysm zones Twilight Highlands or Vashj'ir, complete the introductory questlines to fix your main city phasing to turn in Weigh Anchor.