As I’m doing the career agent missions, it says my standing with them have improved. However it also says my standings for someone else have improved by deviative or something like that. If you get standings for completing missions besides standings with the agent, is there a notification of who else your standings improved with?
Standings are shown on the Interactions tab of your character window (same window that has your skills). You can see all of the factions, corporations, and agents with whom you have standings. When you do an agent mission, the agent gives you a modest standing increase, and their parent corporation gives you a derived, smaller increase. If you do storyline missions, the parent faction also gives an increase, factions friendly to the parent faction get a derived increase, and factions opposed give a derived decrease. Training the Social skill will up the amount of standings change for each mission.
Obligatory EVE Uni wiki link: NPC standings - EVE University Wiki