This page of the NieR Automata game guide explains in detail how to reach the roof of the building in City Ruins related to the Robo Dojo quests and the machine known as Father Servo. This is problematic, as you have to perform special actions in mid-air.
The building in question is located in the City Ruins, specifically near the Desert Zone entrance.
Once you reach Chapter 5 of the campaign, you'll notice a marker in this location signifying that you can accept the first quest - it is shown in the attached screenshot.
You cannot reach the roof of the building in the typical way, as there is no ladder or stairs in the area. Instead, look around the area behind the bus wreck pictured in the screenshot. Use multiple double jumps to reach the roof of the building adjacent to the one with the quest marker.
Direct your attention towards the water tower from the attached screenshots and use a ladder or double jump to get to the top. You will be able to see your destination from here, namely a single machine standing on the roof of the neighboring building.
It may seem to you that the neighboring roof is very far away, but there are certain move combinations you can perform mid-air that will allow you to cross the required distance.
We recommend one of two move sequences:
- Start sprinting (R2) on the water tower -> quickly press the jump button (X) -> press the jump button again (X) -> dash in mid-air (R2).
- Run normally, then perform a double jump (X, X) -> bounce off the pod in mid-air (R1 X) -> dash in mid-air (R2).
Each of these methods should allow you to land safely on the roof and reach Father Servo in order to initiate the first Robo Dojo side quest. We've described all the quests from this line on the City Ruins page in the Side quests section of the walkthrough.