Could you please provide the copy of this form?

There is no "form" as such. Write the clerk, referencing the case. Demand a jury and pay the fee. I suggest you hire a lawyer if you intend to try the case to a jury

I am not intending this to be legal advice, because I don't know the particulars of your situation.

The form is simply a "Request for a Jury Trial," and a jury fee must be paid to your clerk's office. If you are undertaking a jury trial you need a lawyer more than ever. You must be sure that the issues to be submitted are jury issues and not Judge issues. Visitation and support are judge issues. Custody is a jury issue. A domicile restriction is a jury issue.

Hire a lawyer. Practicing law is more than just filling out a form.

In addition to the information my colleagues have given, your written jury demand must be timely filed, and the fee paid, not less than 30 days in advance of the day your case is set on the nonjury docket. While there is no specific form, you will want to familiarize yourself with the Harris County Law Library where you will not only find a format for demanding a jury trial, but also jury charges/questions. You should seriously consider hiring an attorney to represent you, as you are about to compound the complexity of your case a hundred fold, which is of course, your right.