When I've had a slight engine knock I changed the engine oil and oil filter and then added some Lucas Engine Oil Treatment to the oil.
The Lucas Oil Treatment helps thicken the oil a bit to help the bearings and other engine parts get lubricated better which helps with the knocking of the engine.
However sometimes your engine may need repair due to the engine knocking as it could be a rod knock which would eventually lead to spun rod bearings.
You then need to have the engine rod bearings and main bearings changed out.
If your engine is knocking I would recommend getting the bearings changed before it leads to engine damage.
The Lucas oil treatment and other oil additives can help temporarily stop engine knocking but you should get the engine repaired before it causes other problems.