5 That's the man whose/who/that daughter I went to school with.

5. That's the man whose daughter I went to school with.

В данном предложении нужно использовать местоимение whose, так как оно указывает на принадлежность (daughter of the man). Можно также использовать who, заменив конструкцию на That's the man who's daughter I went to school with.

Ответ: That's the man whose daughter I went to school with.