knocking when going over bumpy roads

With the car parked on a flat surface, engine off.
Go around to each of the 4 corners of the car, if it has bumpers that you can stand on do so, then jump up and down on the bumper corners listening for which corner is the loudest, at least that way you can narrow it down to 1 corner, then jack it up from the frame on that one corner, place a jack stand under the frame and lower it down until it just sits on the jack stand and jack at the same time. Then reach and grab every suspension part, brake part and steering part that you find and as hard as you can with your hands, push and pull and twist and wiggle and listen, look if anything moves or makes that noise.
If and when you find out what it is post the name of it and/or post a photo of it.

I am not a.mechanic how can I jack it up?

jacking a car is hard enough to explain in person. Rather than you getting hurt, perhaps you should just go to a shop and have them listen to the noise and test drive or whatever they want to do.