Which of the five main religions practices monotheism?

Im assuming that your talking about the 5 largest, but depending on what you define as "Major", this can be answered differently, but ill do my best.

Chirstianity- Monotheistic

Islam- Monotheistic

Budism- Has no deity

Hinduism- Polythistic

Confucism- Has no formal deity

Judaism- Monotheistic

So if that's what you mean, techniquely 3.