For a test sequence I want to get the following information:
First, all decisions for a CTU are made when
m_pcCuEncoder->compressCtu( pCtu ); is called in TEncSlice.cpp
pCtu is of type
TComDataCU, so if you have a look at TComDataCU.h, you can see all the information that is contained in the object (depth, partition size, prediction mode, information about motion vectors, etc.)
To access this information, you have the functions
getMvField and so on.
Concerning the second part of your question, where to modify the above parameters depends on what you want to achieve. For example, if you modify the depth of your CTU before
m_pcCuEncoder->compressCtu( pCtu ); is ran, the values you have changed will be overwritten by this function...