How do I ground a neautral buss bar in a square D panel

It depends on whether it's being used as a main panel or a sub-panel and specifics of the electrical code where you live. To make sure we're solving rather than making a problem, I'd suggest you contact your local electrical inspector and show him/her the model panel you have and explain the distribution system you're putting it in. After all, the inspector will have to approve the job when finished so asking in advance might save you a lot of rework.