Entrepreneur is a French word, and the stress falls on the end, like many French words in English: NUR. The first syllable has a lighter secondary stress.
The word is borrowed from French entrepreneur, a person who undertakes something. It is built from entreprendre, to undertake, and the ending -eur, which names a person who does an action. English says the ending as ur (NUR), like the end of amateur and chauffeur.
The tricky part is the middle: truh-pruh. Say it slowly, then speed up. The first vowel is not en: it is ahn in the US and on in the UK, and the n is a normal English n.