From what I've heard, the BQ at DHL is quite similar to the Eurowings BQ at Interpersonal. You can find some good information about it here:
Eurowings careers
Bottom line is: Skytest is recommended and you'll need to brush up on your ATPL knowledge. Apart from that, Easy Flighttraining updated their IP BQ products extensively over the last months maybe you could also have a look at them.