From the documentation: "Questionnaire is a separately identifiable Resource, whereas the individual questions are not.". What is the best strategy to identify individual questions?
a. Can I maintain individual questions as single question questionnaires and embed them in a container Questionnaire?
b. Is there any other way to maintain questions separately and refer them in a container Questionnaire?
The DataElement resource would allow you to define questions separately and reference them. There's an extension on Questionnaire that lets you point a question or a group at a data element. Good practice is still to include the question text, data type, etc. in the Questionnaire instance in addition to pointing to the data element to ensure the questionnaire makes sense to systems that might not understand the extension or have access to the data elements, but it's technically legal to have the question only contain a link to the data element and nothing else if you're confident the consumers of the Questionnaire will know what to do with that.