What to expect from an e-bike service? My e-bike manufacturer recommends a service every 1000km. Tomorrow I'll bring my bike to the shop where I bought it for the first service. I already had a mini-service for free at around 300 km in which I don't know what they did exactly, probably some fine screw tuning.

My bike is a city bike built by a reputable manufacturer. I ride it nearly everyday to work. The city has some serious hills.

What can I expect the shop where I'll bring my e-bike will be doing for this ~1000km service? (And will it be the same for every 1000km services in the future?)
The first free service is usually just to account for "bedding-in" from new. They originally build up and tune the bike with all new components, but as you ride it for a few months, it's common for cables to bed in a little more snugly to their fittings as well as for bearings to push into the frame a little more, requiring the components on either side to be tightened up. The bolts on the bike may be a little loose from all of this, so it's always a good idea to get it fully checked over once it's been ridden for a while. 

After 1000 km, it would be checked over for all of that as well as for the general wear and tear. Components requiring cleaning and lubricration will be inspected along with any bearings. Depending on motor position, ebikes might wear out a drivetrain more quickly or require wheels to be trued more often. If you know how to clean and lubricate your bike and measure the chain wear, it's unlikely to need such regular maintenance, but the recommendations tend to be based on the worst case scenario. Someone who rides in all weather, locking it up outside during the day and just puts the bike back in the garage every evening without cleaning it can extensive maintenance within 1000 km.

To minimise maintenance required, there are some basic things to do at home. If the bike gets dirty, clean it off, taking care not to leave it soaking wet for a long time afterwards. Regularly (every 300km or so) degrease and relubricate your chain and pump up your tyres to the correct pressure. An honest bike shop will usually take a look at a bike to tell you whether any more work is required at the time. Unfortunately it can be hard to know how honest your shop is of you aren't an expert, so you should ask your friends for their opinions on the local shops