Oil pressure light came on when braking then started knocking

Hello, the first thing I would do is shut the vehicle off as soon as possible -- safely -- and check the engine oil level. The engine oil level may be too low, causing oil starvation to the engine, and ultimately knocking from a lack of lubrication. Add oil to the "full" line of the engine oil dipstick once the oil in the engine has a chance to drain back into the oil pan -- wait 15-30 minutes. If the oil level is good, then you could have some other internal engine issue causing low oil pressure. Diagnostic testing with a skilled technician is needed.