After heading back to Goku's house and talking with Chi-chi you will be sent to Kame House , there you will talk to Krilin ( there will be a red " ! " sign in his head , marking a main mission ) , after that you go to the training site ( a blue shining circle on the floor , to the left of Kame House ) and you will fight a simulation against Krilin , if you beat him you will get the super attack " Consecutive energy blast " and the achievement.