Does anyone can suggest protentional research question for dissertation. Topic will be "Global cities as subjects/actors in international relations ?''
first you have to remember that the research question should be exactly what worries you, bothers you, or makes you question. We may randomly try to ask a question for your research, but that doesn't mean it will be suitable for your job.
For example, I would ask the following: How do global cities relate to an international dynamic? In this context, can cities be considered "subjects or actors"?
Obs.: In my view, it is much better to try to analyze the agents that produce urban space, and then point to cities as subjects. Because this idea is really not very cool. Cities are a representation of those who build them, whether social classes, companies, industries, landowners, etc. Or even the financial system, excluded social agents.
here some work that might help you:
Article THE URBANIZATION PROCESS AND SPACE PRODUCING AGENTS
Article Sustainable development with environmental, social and gover...
-Future Cities: Digitally-connected, Smart, Sustainable, and Green (DSSG)
-Strategies for improving urban livability(The need for multi-dimensional focus to optimize livability and safety of the urban spaces provides scope and challenges alike to scientists, administrators, and policymakers).
-The trends and challenges of ubiquitous computing in smart cities and to promote further research.
-How Russia influences the fragmented EU.
-International politics on feminism- Analyzing the constant efforts for ensuring gender equality worldwide.
Maybe it is worth to take a view on litterature - ex. Curtis's Global Cities and Global Order (2016) before formulating your research question, which seems quite general to me - and as you see by the title of the book above, already treated.
As said above, you may find an specific sector or maybe an specific city to work on, but only once you've done a deep state of the art. Reading will allow you to identify your niche and then your research question.
I am adding an exemple on how to take the question - a study from CIDOB by Curtis.
Hope that helps, and good luck with your dissertation!