My 2005 XT forester knocks when I go over bumps ( speed bumps / eneven road surfaces) and looking for advice as to what the most likely cause would be. I have already changed the drop links and was going to do the roll bar bushes next, what do you think??

bushes or struts i would think

Strut top-hats or struts, lower ball joint !

need jack front up & give all joints, bushes good inspection. If nothing can be seen then removing struts for inspection maybe needed.

I'd go for lower ball joint first.

Don't forget your anti roll bar bushes a knocking from the front is more likely to be the ARB bushes easy check, screwdriver between bar at bush and the frame pull on screwdriver if a lot of movement it is them, you can check your bottom ball joints just as quick jack front of car one side at time about inch of floor get bar under tyre and look at the ball joint as you leaver on the tyre if you see the join moving replace drop ca and do other side.

If it is your ARB bushes replace front drop links as well as part of the job, top struts easy to do as well jack car on under frame so that leg is extended and pull on the top of the leg as best you can from under wing if it moves then replace but do both false economy to just do one of each problem.

Paul