Since the knocking is affected by road conditions and you didn't mention engine/wheel speed, we can safely assume its a suspension problem and not a drivetrain problem. If its knocking frequency went up as you sped up you might suspect a rotating part such as wheel, axle, CV joint, etc.
Since this is getting worse, you can safely assume it is wearing more. As these wear, they tend to start wearing faster - meaning once they start going bad they go bad faster and faster.
So, you should look at the wear parts of your front suspension. Common ones are bushing and ball joints. The weakest link in there is the stabilizer (sway) bar link. Another might be your front struts failing.
To quick and dirty test the struts, get someone strong/heavy to push down really hard on the front right corner of the car bumper. Push down ONE time and release really fast. Maybe even step onto the bumper and jump down once as you jump off. One big push down and release. Working shocks/struts should bounce up then down once. Weak or failing shocks will bouncy bouncy bounce.
What I would do is Jack the car up and remove that wheel. Securely block and "stand" the vehicle so its rock solid stable. You can visually inspect through the wheel well and from underneath. Look for oil leakage around the strut which could indicate the strut seals failed and wore out.
Look at the bushings for missing rubber - it can be brittle and crack-y looking if older but there should be rubber in there.
Most importantly, inspect the rods that have ball joints. There is a thin straight vertical rod with a ball joint on both ends. That should be snug between its two mounts. If you can wiggle it or push it, you've found your problem.
2007 S60 2.5T AWD (Daily Driver)
2001 S60 2.4T (Spare Car)
1995 850 2.4 (Daughter's)
2005 S40 2.4i (Bought New)
1986 740GLE 2.3(First Volvo)