Even though you can kill the job - as per other responses - using dsjob to stop the job, this may have no effect because the After statement has been issued synchronously; the job is waiting for it to finish, and (probably) not processing kill signals and the like in the meantime. You would be better advised to work out why the After command is taking too long, and addressing that.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…