There are a total of five jobs that can be completed throughout the game. The following are the jobs and their locations. Note: You cannot do Horse Breaking jobs until you have completed the "Wild Horses, Tamed Passions" mission. You cannot do Night Watch jobs until you have completed the "New Friends, Old Problems" mission.

Blackwater Night Watch (located at the half moon icon near the bar in Blackwater)
Chuparosa Horse Breaking (located at Chuparosa in Mexico)
Chuparosa Night Watch (located at Chuparosa in Mexico)
MacFarlane's Ranch Night Watch (located at MacFarlane's Ranch in New Austin)
Ridgewood Horse Breaking (located at Ridgewood Farm in New Austin)