Here is the full list of all 27 Riskers achievements.
Complete all achievements
Kill an enemy while jumping/sliding over an object
Kill an armed enemy unarmed
Complete the game 100%
Unlock brass knuckles
Find all hidden posters
Destroy 100 cars
Find the inflatable duck
Run over 50 people with a police car
Complete the main story missions
Kill Shuba
Kill Thomas
Kill 50 people with a baseball bat
Kill Dino
Kill 10 enemies with a chair
Smash a window with a chair
Complete all side missions
Complete all time attack challenges
Complete all challenges
Complete all shizo challenges
Complete all race challenges
Steal 100 cars
Achieve the fastest car speed
Kill 100 cops
Kill 2 people with a single sniper shot
Kill 4 or more people with a single grenade explosion
Punch and run, have 3 or more people after you