The questions they ask will mostly be the same questions you were asked on your security questionnaire, with a few added questions related to counter terrorism and your overall suitability (blackmail susceptibility, honesty, integrity, etc). If there are any issues present in your background (such as drug use or foreign contacts), the investigator will ask probing questions to ensure they have the full story of what happened with the issue. Don’t fret, they want to ensure they have the whole story for the adjudicators to make a decision on.
As far as personal questions, only the areas which would affect your suitability are explored. Your sexuality and health should not even come up unless there is an issue relating to it. They do ask the same questions from your security questionnaire regarding your mental health, but do not care if you have a disease or poor health.