Trump hasn't done civilian Apprentice properly for 8 years now - there was one series in 2010, which tanked, where the gimmick was that every contestant was unemployed or had been hit hard by the recession (this was the one where there was no job at the end, although he made a decent fudge at pretending there was going to be one) but it's all celebrity editions now, where the contestants take part to earn money for charity (either via fundraising tasks or with funds subbed in by task sponsors/NBC). Trump's there now for the name value, he has no real input or investment beyond deciding who get fired.
Before the change, people applied to get on tv, or work in tv, or for the networking opportunities they'd get or simply I guess, to get a big wage for doing very little at the same time as being able to carry on doing other work. Trump was there for the attention and because he would have been paid a hell of a lot of money to do the show, American tv being what it is. They've actually attracted a fair few people who've gone on to be successful, although I doubt any time they spent with Trump had much of anything to do with it. In media terms someone like Rebecca Jarvis would be a good example I guess - she finished runner-up in Series 4 and she's now (last I checked) the Chief Business and Economics Reporter for ABC News, which in terms of prestige is far higher than anything Hopkins could aspire to.