I'm not sure what you mean by "add up to the subject." And do you really need to connect them all? The correct approach has to be based on what is inspiring you to go into this field. What is it? Some people are passionate about education as the salvation for humanity, and others are passionate about psychology so we can understand ourselves. What drives you?
Whatever it is, it's where your energy is. Do not try to formulate a hypothesis. Just read some great, recent articles related to these two interests you mentioned.When you read the articles, some of them will probably give an overview of the current state of some aspect of investment banking. That is your way in. Get in touch with an aspect of investment banking that fascinates or motivates you.
Then, get very knowledgeable about the research methods available to you. You'll have to do a lot of reading! :-)
The goal is to get knowledgeable enough about research methods that you are able to easily choose a good one to use to solve a real problem or improve practice in your field.