This capability has only recently been made available in Survey123 Connect for ArcGIS. The version I'm working with is 3.0.142. If this solution does not work for you, upgrade to the latest version.
When you create a survey, you will need to make sure your field names are all lowercase. If you have a question that you only want to be required conditionally dependent on the answer to a previous question, ESRI has introduced Form Expressions for this purpose.
When writing a survey question, you now have three options with regards to the required column:
- blank: Not required
- "yes": Required
- Form Expression: Conditionally require using an If Statement. The If Statement is case sensitive!
To address the example asked in the question, the If Statement would look something like this:
Here's what the form looks like in Excel:
Here's what the form looks like in action, with each yes and no selected: