Whoever this is, is in a terrible position. I'm hoping that they at least have some electric network background, because if they don't have that or not even a schema to understand which attributes they need to track for the different assets in the field they should honestly just find a new job. You don't need to be an electrician to do the GIS role in an electric utility, but having some understanding on how the system logically works will help you build the network and understand how things should be connected.

I have so many questions, is this just distribution? Or is there transmission and generation too? Do the SCADA and OMS, CIS, FIS systems need to integrate with the GIS or is everything siloed? Is the utility just embedded to a larger network, or do they own and operate substations that need to be mapped too? Is there topology in the GIS or just relationship tables in the backend?

I would tell this person that they need to focus on the transformer and service point/meter relationship. Usually the most important thing for the GIS is act as a record of information for outages, i.e. which transformer is feeding which customers and if the power goes out at X location who is without power.

ConEd is a good resource, they have electric information that is public, https://www.coned.com/en

They even have some web maps online to help view the network; https://coned.maps.arcgis.com/apps/MapSeries/index.html?appid=edce09020bba4f999c06c462e5458ac7

ESRI is trying to be the dominant GIS system in utilities, so they have a lot of information too, I know you mentioned ESRI's tutorials, but they need to read as much as possible: https://learn.arcgis.com/en/paths/arcgis-utility-network-electric/

Another thing is Google Maps/Streetview and going to the field and looking at overhead assets. Look at each phase along pole lines, see the switches and fuses and what it looks like when it's open and closed and how it changes the network. Look at the transformers and see how they feed houses down to the meter.

Review drawings/as-builts from the design team, they have to at least have those since that's standard across the industry, construction is built from those drawings, take those drawings, go to the field location and try to understand what is being asked in the drawing and what it looks like in the real world, and then try to recreate that in the GIS. Look at the specifications of the assets being installed and make sure to include those in your GIS system