My father wants a capable assistant to help with his work.

Literal

Father [topic-は] work [object-を] help [for him-てくれる] capable assistant [object-を] wanting.

有能な助手 (capable assistant) is modified by 仕事を手伝ってくれる (who will help with work) as a relative clause. 欲しがっている uses ~がる for third-person desire.