Can anyone suggest for me a topic in Finance for PhD research?

Some current topics of interest in Finance are auction and game theory; gambling and sports (University of Salford); employee satisfaction and employee working environment; corporate culture; corporate and CEO governance; and corporate social responsibility and "green" responsibility (ECSP Europe Business School). Other topics of interest in Finance include business failure and bond ratings; health and social well-being; employee motivation and green behavior; and supply chain factors (University of Salford). 
One way to discover topics for Ph.D. research is to examine the areas of research being done by professors at various universities. As with the University of Salford in Greater Manchester, England, professors tend to publicly list their areas of research interest and their latest research publications. These can be used by Ph.D. candidates to inspire ideas and trigger areas of interest.
Following the global financial collapse based on credit-rated mortgage derivatives and as a result of such things as the expansion of gaming theory, the burgeoning needs and costs in healthcare, and the attention given to corporate culture consequent of CEOs' and millennials' behaviors, relevant new topics in finance have come to the fore for the purpose of examining these areas of finance.
[The topics I cited above come from the publicly described research of Professor David Forrest, Dr. Jia Liu, and Professor Hassan Yazdifar of the University of Salford, UK, and Professor Alberta Di Giuli, Professor Michael Troege, and Professor Franck Bancel of ECSP Europe Business School.]
https://iveybusinessjournal.com/publication/the-millennials-a-new-generation-of-employees-a-new-set-of-engagement-policies/