Travel by Car: The driving distance between Hannover and Mostar is about 1.650 km, and travelling time is about 15 hours. Recommended route goes trough Croatia, Slovenia, Austria via highway where tool fees apply. In Germany highway is free of charge.
Travel by Bus: If there are direct buses from Hannover to Mostar, timetable and price tickets for buses you can check here. Alternatively it is possible to travel via Sarajevo or Zagreb in Croatia.
Alternative ways of travelling from Hannover to Mostar:
Travel by train: From Mostar there is a possibility to travel by train to Zagreb (via Sarajevo), and then continue with international train to Hannover (via Munchen).
Travelling by train from Mostar to Hannover is much slower that travelling by bus or car, as trains in Bosnia and Herzegovina and Croatia are very slow. More information for travelling by train in Bosnia and Herzegovina you can check here.
Travel by plane: There is no direct flight, but there is option to fly to Sarajevo or Split in Croatia.
Map with buses from Mostar: