For each chapter you can do maximum of 2 objective, one for the playstyle and one for the 100% loot collection. When you press f1 (by default) > "Player Progression" > "Statistics" while playing a chapter, on the left side you can see objectives for that mission. You can only have one playstyle objective completed per chapter. Exceptions are client jobs, during wich you can accomplish all 4 objectives most of the time. Amount of completed Thieving Objectives is labeled in the statisctics menu on "Overall" tab.