This has been flagged as missable since it is possible to complete the career and fail to achieve 20 Sponsor Objectives BUT highly unlikelyAt the beginning of each new season of the Career in WSR you are given the option to pick some Objectives from various sponsors to try to beat, you are given 3 slots at first and are given more as you progress
Make sure to pick the easiest objectives that you think you can beat (such as reach a certain speed, drift certain feet, etc) as to make this trophy easy to unlock.
If you forget which objectives you have picked you can press

whilst in your garage.
Providing you complete every objective you pick this should unlock during season 3.Unlocking this will also unlock

The Mo Money, No Problems trophy in GRID 2 worth 22 pointsYou've gone above and beyond the call of duty and completed 5 career sponsor objectives.