Secret Service

Yellow lines above the guest's head means they want food.

Red lines above the guest's head means they want a drink.

When you pick up the disguise you will want to go out the left side of the doors as the right side won't have the mobs. Once on the left side you'll walk around and there should be yellow dots on your minimap and the person should be outlined. Go up to them and click them and you'll see either food or drink so you know what to serve them. You can also find puddles that look like a metallic silver on the ground that you can go up to and clean. Sometimes a rat will randomly spawn that you can punch to death.

If you complete the world quest without losing the disguise such as being seen by the guards then you'll earn the Caught in a Bat Romance achievement. If you want to make it easier you can just stay in the starting room as well and just punch rats as they spawn. It'll be slow, but you won't have to run around guessing and can earn the achievement at the same time.

This quest is located up on a high area, not down on the ground. In order to reach its location:

The closest flight path is Old Gate, Revendreth. If you do not have this flight path:

1. Get to the elevator located at 63.5, 40.9 (ground level) and take it to the higher level.

2. After you have taken the elevator up to the higher level, get to the stairs located at 62.5, 37.5 and take them up. Note that there will be a few hostile mobs in the area.

3. After going all the way up the stairs you will be able to access the Old Gate flight path and nearby friendly NPCs; from there, take yet another flight of stairs up, starting at 60.3, 38.7

4. At the top of these stairs turn right and continue in the direction of where the quest is marked on your map (there will be more hostile mobs on the way). When you get to 57.4, 33.4 take the elevator upward. Once you reach the top and step off the elevator you will be in the quest area. You will be facing a building, and just inside it you will find the yellow dot indicating the Servant's Basic Kit that you have to click.

I hope that this helps.

(Please note that these directions were posted before flying was possible in the Shadowlands - and, as such, they explain how to get to the quest area without flying)