Whenever the car hits a bump in the road a knocking sound under the drivers side occurs.

Check if the muffler is in place and if it is moving...

Possible sources include a blown shock, worn wheel bearing, worn tie rod end.
A bad shock can sometimes be located by bouncing one corner of the car at a time and watching how that corner settles; if released at the bottom of the stroke, the car should not do more than rise above level and drop again. Any more action points to a shock that isn't tight anymore.
A worn bearing can often be found by grasping the top of the tire and checking for play by pushing it in and pulling it out again; there shouldn't be any noise or noticeable play.
By having someone at the wheel, worn suspension points will show play as the wheel is turned back and forth at a medium pace; look for suspension points with abnormal movement and don't respond to a reversal of turn direction instantly.
The last two problems will be seen if a wheel alignment is attempted and will cause the measurements to vary from one time to the next.