You should be able to use the same code mentioned above and add few more lines
IIndexWord idxWord = dict.getIndexWord("dog", POS.NOUN);
IWordID wordID = idxWord.getWordIDs().get(0);
IWord word = dict.getWord(wordID);
ISynset synset = word.getSynset();
String LexFileName = synset.getLexicalFile().getName();
System.out.println("Lexical Name : "+ LexFileName);