Question about Gardena Water socket

You probably mean whether the pipeline is fed through the water socket - i.e. has an underground water inlet and outlet.
No, the water socket is always the end point. If you continue the pipeline after the water socket, you must install a branch to the water socket using a T-connector.

The Gardena socket has a pressure-resistant end closure. This only opens when the water hose is plugged in. If plugs are attached to both sides of the hose, a "daisy chain" should work. However, the second coupling (hose to socket) would always have to be disconnected without pressure.

I must correct myself: this is the outlet for the water. You must use the junction box as the input: Gardena junction box

Or as a set: Gardena Start Set for Garden Pipeline

This is no problem and is also one of the ideas: to have a connection in the middle of the lawn. You can also install 3 or more water sockets. Or 2 water sockets and a sprinkler. Of course, this has an influence on the pressure and flow per time. Important: the water socket does not have a drain valve. This should be purchased and installed at the lowest point (i.e. valve and Y part required) so that the water does not remain in the pipe in winter.