string  usd_relationshipnames(<stage>stage, string primpath)
This function returns the relationship names that are available on the given primitive.
When running in the context of a node (such as a wrangle LOP), this argument can be an integer representing the input number (starting at 0) to read the stage from. The integer is equivalent to the string form referencing a particular input, e.g., "opinput:0".
The path to the primitive.
String array containing the names of the primitive’s relationships.
// Get the relationship names from the primitive. string relationship_names = usd_relationshipnames(0, "/geo/cube");