Hi Yi. This question is too vague. It would be best if you started focusing on a particular theme you have the desire to research, read their limitations/suggestions for future studies and then you can start to have a glimpse of what you might explore. There are other ways (identifying methodological gaps, new theories or applications and other areas). Still, you need to read to check out not only their novelty but their importance to theory development. I strongly advise you to read "Kock, F., Assaf, A. G., & Tsionas, M. G. (2020). Developing courageous research ideas. Journal of Travel Research, 59(6), 1140-1146." It won't give you a specific topic, but it might open your mind to potential ways to develop your research.
Tourism is multi-facilitated discipline. It is just like sponge. It is better to focus any of the area. Others scholars' opinion is also valid in context of your question.
The question is too general as tourism is a broad topic
So I suggest that first you decide on what perspective of tourism field you would like to do research. If it is from marketing view then you will have different theories and methodologies (study population would be different…)
if it is from the local community then you may have different related methods and theories (for example you can study from residents‘ point of view… )
Once you decide then you can go for the research gap/problem through studying the lastest articles and finding the limitations and study for future research as the other scholars mentioned.