what does (reading) refer to and is this word an adjective???

In your sentences, the participatory is used to shorten a subset. This use of Partizip 1 and Partizip 2 is found almost only in literary texts:

1. Participation 1 (active + simultaneous): While her an exciting book las, did not notice that it began to rain.
2. Part 2 (here: intransitive verb, active + past: After we go to the destination had arrivedWe went to the hotel.

Partizip 1 as a Gerundiv:

This is very serious to takinge Sickness. = This is a disease,

• the very serious to take is.
• the man very serious to take has.
• the man take very seriously must:.
• are taken very seriously must:.

It’s about a hard one to removeen Tumor. = It is a tumor,

• the only hard to remove is.
• the and only hard to remove leaves.
• the man only hard to remove can.
• which is difficult to remove can.

In many (sach) texts become Participational attributes used instead of a relative. This takes place especially when a node has further attributes in the form of a genitive or another relative set. The partial construction is then the so-called left-attribute, because it is in front of the, i.e., on the left of the nomen, and the genitive or the other relative position is the legal attribute, because it follows the described nom, i.e. stands to the right thereof.

• P1: The parents were waiting for the with more than 60 minutes Delay of land São Paulo machine in which her daughter sat. = The parents were waiting for the machine from São Paulo, the more than 60 minutes late landed and in which her daughter sat.
• P2: We had to repaired only last week Take the car back to the workshop. = We had our car, the last week had been repaired, get back to the workshop.

And here’s another poem Bertolt Brecht: “Questions of a Reading Workers”

https://www.youtube.com/watch?v=KxvRQGvurvA