I have a 23-year-old special needs child

There has been a conservatorship in place since she turned 18. How do I address this issue in a divorce?

I suggest raising the issue under Item 11c of the Petition (FL-100) if you’re the Petitioner, or Item 11c of the Response (FL-120) if you’re the Respondent. You can ask the Court to declare the child as incapacitated and unable to be self-supporting and determine adult child support under Family Code Section 3910. You will then want to actually file a motion to request that support be established.