What part of the German workforce is Auszubis and Praktikanten (A&P)?
What part of the workforce in the new Bundesländer? What is the
average salary of the A&Ps? What part of them do their work for free?
What part of them do their work for 340-basis? How many (percentage)
of them are employed after their first A&P? What are the positions of
German political parties on the subject of the (ab)usage of A&Ps in
the workforce as cheap labour?

It seems that you are not very familiar with the German situation
regarding labour.

"Auszubildender" (short: Azubi) might be translated to "trainee".

This term is defined by law. The aim of a "(Berufs-)Ausbildung"
(apprenticeship) is a state recognized cetificate.

"Praktikant" is a loosely defined term for somebody working in a
company - often besides his involvement in university or similar
education. Sometimes, "Praktika". It reaches from 2 weeks up to 6
month.

besides local traditions, there is no difference between the old and
the new Bundesländer.

There is no such thing as a "average" salary for "A&P". the salary for
Auszubildende is defined in a contract. Most contracts are restricted
to "flächentarifverträge" which apply to all companies in an area.

The 340 Euro-law does not apply to Azubis. Salary for Praktikanten
reaces from 0 up to x > 1000 Euros per month (remember the old days of
the new economy?)

The general aim of the Ausbildung *was* to stay within the company.

Abusing Azubis as cheap labour sounds strange. there are better ways
:)