Hi there,
1. Make sure that you have installed the plugin Smart Search - FAQ Book Pro Questions that indexes questions.
2. Now run the indexer again and check that questions have been indexed.
3. Create a filter in the back-end where the Content type is set to FAQ Book Pro Questions and assign the filter to the appropriate group (field Group).
4. Now open the Search Form in the back-end and make sure that the correct group is selected in the field Filters > Filters group (this should be the same group as the one in step 3).
5. Now you should be able to search for questions in the front-end.