How can a relative studying in Hungary, who has lectures from 8 AM to 6 PM, perform the Dhuhr to Isha prayers that overlap with his lectures? Is it permissible for him to combine and shorten, or just to combine?

Prayer is obligatory at its prescribed times, especially the 'Asr prayer. A Muslim must be diligent in performing it on time. However, if this becomes impossible after making every effort, then it is permissible to combine two prayers (Dhuhr and 'Asr, Maghrib and 'Isha) when there is difficulty or hardship, based on the hadith of Ibn 'Abbas, may Allah be pleased with them both. The prayer should be performed in full, not shortened, as shortening is specific to travel.