How many of his risk factors for type 2 diabetes can mr. joiner control?

The correct answer is 2.

Type 2 diabetes is a lifelong condition which involves high levels of glucose in the blood and is caused by irregularities in insulin. There are specific factors which can increase the risk of developing type 2 diabetes and these are excessive weight and fat tissue, old age, family history of type 2 diabetes, race, reduced physical activity, high blood pressure and others.

Mr. Joiner's age and race could be considered risk factors since the older you are the more increased is the risk. Also, African American people are found to be at higher risk for type 2 diabetes. However, these are risk factors which he cannot control.
The risk factors that Mr.Joiner can control are his reduced physical activity due to his sedentary life and his weight (since his BMI indicates that he is overweight). Most probably he should also try to have more healthy eating habits, by cooking healthy meals at home instead of dining out so often.