Can I sue for malpractice or wrongful death for my son who commited suicide after not getting help or medication in a mandatory psych hold facility

The success of a lawsuit in your situation would depend on many different factors surrounding your son's treatment.  A good place to start would be to document everything and make a timeline of events so a lawyer can look over things to give you a more in-depth opinion.  There have been similar cases filed after people in custody have committed suicide.