If parents have joint custody and one parent is getting married and wants the child to attend but other parent says no what can be done?

It's too bad when divorced parents make their child carry the burden of their animosity for each other. To parent who refuses to get along, don't think your child doesn't feel it. You may be in for a surprise when they're all grown up and remember your bad behavior.

You haven't provided any detail about any factors that would explain the "no" in this case. Is there a lot of traveling involved? Is the child particularly young? Does the parent who is getting married have a problem with alcohol? If there are no such extenuating circumstances the child should be allowed to attend the wedding. It can be assumed that the parent who is withholding the permission may get remarried at some point and will want the child to attend that wedding.

If the wedding is planned on a non-visitation day and the other parent refuses to allow the child to attend, all you can do is seek a court order.