So far, I've found that you can gain these attributes in the Gym.
There may be more, but these are the one I've found
IN THE WEIGHT ROOM:
+1 Stamina = Vertical Jump
+1 Reaction Time = Gatorade Hand-Eye Tests
+1 Hustle = Agility Ladder
ON THE PRACTICE COURT:
+1 Free Throw = Practice Free Throws at Free Throw Line
+1 Hands = Drill Completion? (got it after completing a drill at team practice.)
More to come.
Stamina and Hustle is random. You just need to do 4-5 different exercises in the gym. Hand-eye test is for Reaction Time, that's correct.
Offensive consistency is gained thru the dribble moves practice (usually on the 4th team practice, approach the assistant coach).
Hands, shot iq, intangibles and draw foul attributes are also randomly gained. It's on the drills (i also got it on the 4th team practice, just use the "practice glitch" to get them to max asap).