Learn English – Appear in the exam or appear for the exam

I would use the following sentence, since the two approaches are for the final step. To me, from which would mean that the two approaches follow the final step.

Object models are reconstructed in the final step, for which two different approaches are basically found: model driven and data driven.

Using a different verb, I could use which.

Object models are reconstructed in the final step, which uses two different approaches: model driven and data driven.

There are three things to consider. The first two are easy: who are you paying? why are you paying?

The third is a bit hard to explain but think of the need for a payment as a thing on its own distinct from the person you are paying and the reason you are paying. This often takes the form of a document like a bill or invoice but also could be more of an idea like a debt or a fee.

Who you are paying and the "need to pay" can be used without "for". In fancy words, they can be "direct objects" of "pay". The reason you are paying should be attached with "for".

"You pay the library."

The library is who you are giving money to.

"You pay for the library card."

The library card is why you are paying. You are not giving money to the little bit of plastic so you do not "pay" it and instead "pay for" it.

"You pay the library card fee."

The library card fee is the idea of needing to pay. You can think of it as a hole you need to fill with money into in order get the library card. Because the money is going into that hole, you "pay" it rather than "pay for" it.