к слову today - When must he work hard?
к слову work - What must he do today?
к слову he - Who must work hard today?
He must work hard today. - выделенного слова не вижу,буду задавать ко всем.
1. When must he work?
2. How must he work?
3. What must he do hard?
4. Who must work hard?
5. Must he work hard?
6. He must work hard today, mustn't he?
7. Must he or she work hard?
