The FHIR downloads page provides a way to download examples (one zip for XML and one zip for JSON).  In the JSON examples download (and not the XML one), there are questionnaire examples for each resource type (seemingly programmatically generated?).

Unfortunately, many of these examples (maybe half?) violate the following constraint:

que-2: The link ids for groups and questions must be unique within the questionnaire (Questionnaire)

I spot-check a couple of them and, in the ones I checked, it seems to be related to the way that the linkId fields are being generated.  For example, activitydefinition-questionnaire.json has multiple linkIds with a value of "

ActivityDefinition.timing[x]._null

"

Similarly, supplydelivery-questionnaire.json  has multiple linkIds with a value of "

SupplyDelivery.occurrence[x]._null

"

I'm thinking maybe the issue is related to the programmatic generation of linkId for choice-type elements?