When an Engineer requests possession of lines outside the Station, say 'Gabelung-Teufessspring PZ - Gleis' is it just the one line in direction of travel which he is blocking or all lines between these locations, in this example 3 lines?

Track possession request only apply to a specific track section, thus not an entire line.

In your example a request is done for the track section of the Pz (passenger track, which is the orange one on this panel) from Gabelung towards Teufelsspring.

The Pz track from Teufelsspring towards Gabelung, as well as the freight track (brown) overthere stay open.

Erwin

Thanks for your quick response.