You can specify the path to ./server/appname directory after appname as the destination, i.e., where the Django app directory structure will be created.
From the startapp documentation:
startapp <app_label> [destination] # startapp command usage
Creates a Django app directory structure for the given app name in the
current directory or the given destination.
If only the app name is given, the app directory will be created in
the current working directory.If the optional destination is provided, Django will use that existing
directory rather than creating a new one
So, you can specify the path to your ./server/appname directory as the destination value.
django-admin.py startapp appname [destination] # Specify destination
What do you need to do?
1. You need to first create a directory, appname, inside /server.
mkdir ./server/appname # Create a directory from the root level
2. Then, run the startapp command to create the app.
django-admin.py startapp appname ./server/appname