Thanks for the support
Ok i wasn't really clear with my question by saying "it disappears or it is only visible in the content zone".
What i meant to say within the first question is that i tried some placements and the following placement moved the part only to the first place of the Content zone:
Other attempts made it disappear (probablly because i used unkown zones in the placement.
using the following: _workContextAccessor.GetContext().Layout.Zones["Header"].Add(shape, "1");
results in rendering the following in the header: ContentManagement.Drivers.ContentShapeResult
Finally i managed to get ik working the way i want by adding the following line of code in my Layout.cshtml in the theme:
Even though it works i still don't know if this is the best way to this.
To clear out my question: I have a custom part which i'm trying to render in the Header zone above the Website logo.