1999 Nissan Sentra KNOCKING WHEN I MAKE A TURN

Sounds like a C/V Joint. If it is, replacing the entire half shaft is better than just repairing the C/V Joint itself. More than likely if you look you will see the rubber boot is split and grease everywhere, the cv will need to be replaced, have this inspected.

THANK YOU SO MUCH FOR YOUR QUICK RESPONSE. DO YOU KNOW HOW MUCH THAT WOULD COST?

First it must be determined that that is the problem. If it is then the part is around 70 bucks plus small insidentells like cleaner and grease ETC. and the job is around 3 hours. Depending what the mechanics' rate is I would expect a 300 dollar bill. If it is the problem, buying the parts yourself and having a mechanic install it can save you money also. This way you will know warranty information also.
If you are remotely mechanicaly inclined this job is not difficult but it does require a special socket for the shaft nut. If you do it yourself I do suggest purchaseing a repair manual like haynes.

Here you go.

https://www.2carpros.com/forum/1998-nissan-sentra-axle-assembly-vt207375.html