Worn front axle and/or front end component.
On a front wheel drive car probably a damaged constant velocity joint clattering
needs new wheel bearings
The knocking noise could be one of several things. The wheel bearing, a worn steering or suspension part, or road debris could be causing the noise.
A knocking noise in the front wheels can be a very serious problem. The knocking noise could be caused by bad ball joints. Bad ball joints can slip off the tie rods and cause the wheel assembly to collapse. This problem should be looked at as soon as possible.
Wheel bearing maybe?
Worn left front wheel bearing.
is it front wheel drive? if so the cv joint is bad
Could be a bad CV joint or bad wheel bearing C.V. Joints need replacing
Assuming it is front wheel or 4 wheel drive, it is worn CV or Constant Velocity Joints. :o)
Assuming this is an older car a knocking noise on turning could mean one of the drive shafts is worn. Other things to check - are the bolts tight on the front wheels, if a very high mileage it could be worn wheel bearings.
Turning right loads the left front wheel of the vehicle, so if you hear the knock when you turn right the bad CV joint is on the left, and vice versa.
Power Steering?