you can inspect ParserState.BuilderData object (ParserStateData)
It has ShiftItems set (set of LRItem) - these are productions that may be shifted in the current state. To get to non terminal:
LRItem.Core.Production.LValue is a non-terminal on the left of the production rule (the owner of the rule)
Note: if ParserState.BuilderData is null - then make sure you disable clearing this field at the end of parser construction. Just find where it is set to null and disable it.