Mano is the latin word for Hand. A common saying "mano y mano" is Spanish for Hand to hand. Usually associated in engaging in throwing fisticuffs with two or more people, usually two. Keeping that definition in mind, a Manojob simply is a slang term for Handjob.
The practice of only having one hobby. Monohobbitious people seem to be happy doing the same thing every day. See also Spod Deadhead Luddite Saddo Colonel Blimp