Any clues what it’s for?

 

area around it is damp, which may or may not be coming from the “clip” part. (Moisture not coming from rear washer pipe).

 

 

Get a shot with the part number fully visible and it'll probably be an easy google.

Something like rear ABS sensor wiring maybe?

Yeah, check out item 4 here: https://skoda.7zap.com/en/cz/fabia/fab/2003-225/9/971-971085/

Thanks, fluid clearly not coming from that

Yep, ABS sensor wiring

google fabia leaky doors

19 hours ago, SkUG said:

google fabia leaky doors

It’s not that, all sealed up!