A Neck injury from wearing a suit? Unless someone tried to hang you with your tie, I see a steep uphill battle. My advice is to find a WC Attorney, because it highly unlikely that the Insurance is going to accept your claim.
I represent Employers, but I can recommend Worker Attorneys in So Cal if you ask.
Standing 9 hours (plus the suit) is not a way to injure a neck. feet or knees, yes; neck, no.
Are you CERTAIN is was the suit and the standing that injured the neck & shoulder? This would lead 99% of adjustors to deny your claim and you'd get zero until you have a Treating physician or a QME write that standing 9 hours lead to a shoulder and neck strain...which is unlikely.
DID ANYTHING ELSE happen in that 9 hour period that resulted in the neck pain? Or was it day-to-day overuse, 9 hours over and over and over, that gradually lead to a neck & shoulder sprain/strain?
If the paperwork is the initial claim form (DWC-1 form), then you need to fill it out carefully and completely. However, consulting with an attorney who practices work comp law could be helpful to you. Why? Well, maybe there are more facts to your case which would better explain nerve injury to the neck and shoulder, other than wearing a suit and tie and standing for 9 hours.
A work comp attorney can interview you by asking you questions that perhaps you have not thought of. For example, if you have some kind of dermatology problem or sensitivity issue which is now made worse b having to wear a suit and tie, or some type of prior neck injury which is now somehow made worse. I would have to agree with my colleagues that just wearing a suit and tie and standing for 9 hours is a tough sell without some more explanation behind it. A consult with an attorney whose practice includes work comp may help you to find that explanation.