I just completed mine a few weeks ago.
It was mostly based around a scenario - cross country flight. Questions about every phase; planning, preparation, pre-flight, flight, navigation, communication, emergencies, lost comms, etc.
Oral study guide is very good for knowledge. Scenario requires practical application of acquired knowledge.
Know the usual items: pilot qualifications, currency requirements, part 61 & 91, speeds, altitudes, airspace, VFR rules, equipment, systems, inspections, etc.
All special emphasis areas but especially ADM, collision avoidance, runway incursions, wake turbulence, and CFIT.
What considerations & information are relevant to plan a flight.
Know what info is in the POH, limitations, w&b charts, performance charts.
What steps are required for inop equipment?
Know how to read and explain metars & tafs, notams, winds aloft, weather charts. Be able to identify weather symbols on the charts.
Icing.
Inadvertent entry into IMC.
Be able to explain most/all chart symbols, airfield info, frequencies, origination & destination airports, route, checkpoints, etc. as you discuss your cross country plan.
Be ready for questions about range, do you have enough fuel, where would you stop along route if you needed fuel? I was given a weather diversion in mountainous area. Required going back to closest airport and staying overnight. Then did not have enough fuel for remainder of flight so had to refuel.
Be able to identify airspace and airspace layers on charts. What is restricted and prohibited airspace? How do you find out who controls it and when it is active? TFRs?
Runway/taxiway signs and markings, runway lighting, light signals.
Night operations.
Hypoxia and CO2 symptoms and remedies.
My understanding is each examiner is different and each exam is different. They try to determine if you have basic knowledge necessary and then explore your limits. I also learned a few things from the examiner during our discussion.
You should be able to have reference materials to look things up. I took every manual I own but only needed to look a few things up in the FAR and AIM, and the POH. However, it was comforting to know the other books were available.
I saw a reference once about preparing for oral exams that stated: memorize the information you would not have time to research when flying, and be familiar with the what you don't need to memorize and where it is located.
Offer to look up info you dont know or are unsure of - dont leave it at "i dont know". If you give an answer and the examiner asks if you are sure or if you would like to look it up, take the offer.
Relax a little. One thing I can say is that it was very thorough but not as bad as I anticipated.
Good luck!