Is this date editable by end user, or you want to set it to the current date and make it read only
Anyhow you can add the field in the form as type=date as in below, this will create a datepicker field
If you want to make readOnly, just add readOnly=“true”, if not default value will be current date and user can select a different one if required.
<Field displayName="Current Date" helpKey="Current Date" name="dateAttr" type="date" value="ref:dateAttr" >
<Script>
<Source>
import java.util.Date;
Date currDate=new Date();
return currDate;
</Source>
</Script>
</Field>
Hope this same field you will reference and use in report parameter for queryOptions as per your need and in the arguments.