Start by climbing under the front and have someone you trust turn the wheel for you. See if the knock is coming from the steering box or somewhere else. Maybe the track bar loose or something like that.
Ive had a front end knock for two reasons that I chased down and fixed: an improperly torqued control arm and a broken front stabilizer link. The cup that held the ball end of the link, broke. The ball end would bang across it when I turned the wheel hard or drove up a driveway ramp or lot entrance.