You may find it difficult to induce the tip-of-the-tongue experience. It takes careful selection of words that are unfamiliar but not so unfamiliar that your participants don't have a clue. What you are likely to find, if you do get the tip-of-the-tongue response, is that people can remember something about the length of the word (e.g. how many syllables), its metrical structure (where the stresses are) and some of the sounds, particularly the beginning and possibly the end of the word (Aitchison's 'bathtub' effect). This tells you that when words are constructed during speech production properties such as their stress pattern and the beginning sounds are important. These aspects of words are also important in spoken word recognition.