The ability to answer technical questions is just a part of the interview. The interviewers are also looking at the candidate's attitude, ability to cope under stress, and how he/she communicates. It's definitely okay to say I'm not sure to a question as I don't think they expect a candidate to know everything. Getting a PPL or even logging a few hours in HK is not easy, but you can still deepen your knowledge in aviation through books, joining CX's I can fly/HK air cadets, and flight simulator. There are online groundschool courses available on the Internet so not being able to go overseas to acquire flying hours is not the be all and end all.
But if you have the opportunity to get flying experience, definitely go for it!
All the best!